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teaching before long became apparent in geological literature. It was first translated into French in an edition which, thanks to the singular erudition of its editor, M. E. de Margerie, has been so enriched with footnotes as to become an invaluable work of reference for published papers in every department of the wide range of subjects whereof it treats. Within the last few months the first volume of an English translation by Miss Hertha Sollas, under the direction of her father, Prof. Sollas, of Oxford, has been issued by the Clarendon Press. The labours of Prof. Suess are thus placed within the reach of all English-speaking geologists in a version which reads more like an original treatise in our language than as the translation of a German work.

That in covering so wide a field as that of the "Antlitz" the author has necessarily had to rely on recorded observations of unequal value, and that consequently the deductions he has drawn may need to be corrected from subsequently obtained fuller and more accurate data, will doubtless be admitted by no one more frankly than by himself. But even in regard to questions which have long been discussed, and regarding which abundant facts have long been known, there is room for different interpretations from those which the professor has adopted. Thus the phenomena of submergence and emergence of land in Sweden and the basin of the Baltic are treated by him in great fulness and with much ingenuity, but he arrives at conclusions strongly opposed to those to which prolonged study has led the northern geologists. This problem is one of fundamental importance in regard to our conceptions of the nature of the movements to which the surface of the globe is subject, and it is much to be desired that some general agreement in regard to it should be attained.

THE RUDIMENTS OF BEHAVIOUR. Contributions to the Study of the Behaviour of Lower Organisms. By Prof. Herbert S. Jennings. Pp. 256. (Washington: Carnegie Institution, 1904.) THE HE author has been for about ten years a careful observer of the rudiments of behaviour which are exhibited by unicellular and other relatively simple animals, and we have read with interest several of his previous studies on the reactions of infusorians and the like to various sets of stimuli. The general impression conveyed was that infusorians and the like gave evidence of an exceedingly simple and stereotyped mode of behaviour-a mere reaction method. When effectively stimulated by agents of almost any kind, the animalcule moves backwards and turns to a structurally defined side of its minute body, while at the same time it may continue to revolve on its long axis. In relation to all sorts of stimuli, the behaviour seemed exceedingly simple and machine-like. But Prof. Jennings has been gradually discovering that the simple reaction-formula does not cover all the facts, and he now gives us news which seems almost too good to be true.

He finds that even among unicellulars "the behaviour is not as a rule on the tropism plan—a set, forced method of reacting to each particular agent— but takes place in a much more flexible, less directly machine-like way, by the method of trial and error." This is a momentous conclusion, notably in relation to comparative psychology. The data are foundationstones for the science of animal behaviour, and the author is to be congratulated on his demonstration that the ways of even very simple creatures are more than series of "tropisms."

In his "Introduction to Comparative Psychology (1894), Dr. Lloyd Morgan told the story of his dog's attempts to bring a hooked walking stick through a narrow gap in a fence. The dog "tried" all possible methods of pulling the stick through the fence. Most of the attempts showed themselves to be " error." But the dog tried again and again, until he finally succeeded. He worked by the method of trial and error; and so, Prof. Jennings now assures us, do the infusorians.

Nevertheless, apart from differences of opinion, which are inseparable from the growth of such a science as geology, and even where one may be most disposed to dissent from the views of Prof. Suess, the transcendent value of his life-long labours is none the less vividly realised now by all who have studied his writings. Their importance in the history of science will assuredly be no less fully acknowledged by the future generations who will gain from them inspir-haviour of higher animals, yet with the simplest ation and enlightenment. Meanwhile, he has the satisfaction of abundant recognition from all civilised countries. The learned societies of Europe have vied with each other in doing him honour, and not the least prominent among them has been our own Royal Society, which ten years ago elected him as one of its foreign members, and in the year 1903 awarded him the Copley medal-the highest distinction which it has to bestow. The "Antlitz" is not yet completed, but the second part of the third volume is far advanced. Let us trust that years of rest and quiet work are in store for the illustrious geologist, and that he may live to finish his work amidst the hearty congratu lations of the many fellow-workers who look up to him as their master. ARCH. GEIKIE.

"This method of trial and error involves many of the fundamental qualities which we find in the bepossible basis in ways of action; a great portion of the behaviour consisting often of but one or two definite movements, movements that are stereotyped when considered by themselves, but not stereotyped in their relation to the environment. This method leads upward, offering at every point opportunity for development, and showing even in the unicellular organisms what must be considered the beginnings of intelligence and of many other qualities found in the main basis of behaviour is in these organisms higher animals. Tropic action doubtless occurs, but the method of trial and error."

This is not the first time that the dawning of intelligence has been discovered in the Protozoa, but on previous occasions the discovery has been reported by casual observers or by investigators unacquainted with the tropisms. Prof. Jennings has made a special

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study of the tropisms, and we find him declaring that it is almost impossible to describe the behaviour of the unicellulars intelligibly without using terms like "perception," "discrimination," and "intelligence." Of course these are used in an " objective sense," and "when their objective significance is kept in mind there is no theoretical objection to them, and they have the advantage that they bring out the identity of the objective factors in the behaviour of animals with the objective factors in the behaviour of man." From our point of view, Prof. Jennings does not strengthen his position by using these pre-occupied psychological terms; "perception of a stimulus, he says, means merely that the organism reacts to it in some way; 'discrimination of two stimuli means that the organism reacts differently to them; intelligence' is defined by the objective manifestations mentioned in the text." But this does not seem to us the sound line of progress; it leads back to saying that the lucifer match perceives the sandpaper on the box. It seems safer, in the meantime, to say that infusorians alter their behaviour, and alter it effectively, in respect to their experience.

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"Stentor does not continue reacting strongly to a stimulus that is not injurious, but after a time, when such stimulus is repeated, it ceases to react, or reacts in some less pronounced way than at first. To an injurious stimulus, on the other hand, it does continue to react, but not throughout in the same manner. When such stimulus is repeated, Stentor tries various different ways of reacting to it. If the result of reacting by bending to one side is not success, it tries reversing the ciliary current, then contracting into its tube, then leaving its tube, &c. This is clearly the method of trial and error passing into the method of intelligence, but the intelligence lasts only very short periods."

With such difficult subjects any evidence of the registration of experience was not to be expected, and the author is to be congratulated on having discovered considerable evidence in support of the thesis that the behaviour of unicellulars is largely a method of trial and error, one reaction by trial and error becoming the basis for a succeeding reaction. This is surely a pathway leading to the high-road of intelligence.

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It is easy to make an inanimate system-a little potassium pill on a basin of water, or a tiny woundup engine on a smooth table-which, once set a-going, will charge against an obstacle, will fail to overcome this, will recoil passively and charge again, and some observers have thought that, mutatis mutandis, the animalcule did little more. But Prof. Jennings has shown that the infusorian, in relation to its experience of "error," changes its little tactics, and changes them again, until it succeeds. In a word, it profits by experience. The very essence of vitality, as Spencer pointed out, is in effective response to environment; but when we find an infusorian "trying one response after another, abandoning those that spell "error," we cannot but feel that vitality has been raised to a second power; it is just beginning to be intelligent. The infusorian, is more than a tropic automaton, it is playing a little game of tactics; perhaps if we could educate

one it would develop the rudiments of strategy. It is, of course, extremely difficult to keep to a scrupulous objective record of what occurs, but we incline to think that Prof. Jennings has supplied what comparative psychologists have been waiting for, namely, quite trustworthy accounts of the beginnings of selective or controlled behaviour.

"The method of trial and error involves some way of distinguishing error, and also, in some cases at least, some method of distinguishing success. The problem as to how this is done is the same for man and for the infusorian. We are compelled to postulate throughout the series certain physiological states to account for the negative reactions under error, and the positive reactions under success. In man these physiological states are those conditioning pain and trial pleasure. The method of and error' is evidently the same as reaction by selection of overproduced movements,' which plays so large a part in the theories of Spencer and Bain, and especially in the recent discussions of behaviour by J. Mark Baldwin. The method of trial and error, which forms the most essential feature of the behaviour of these lower organisms, is in complete contrast with the tropism schema, which has long been supposed to express the essential characteristics of their behaviour."

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Instead of referring in detail to the author's studies (1) reactions to heat and cold in the ciliate infusorians; (2) reactions to light in ciliates and flagellates; (3) reactions to stimuli in certain rotifers; (4) the theory of tropisms; (5) physiological states as the behaviour of lower determining factors in organisms; and (6) the movements and reactions of amoeba-we have sought to explain the chief result of his studies in the infant school of life, and to emphasise its importance in relation to the general theory of animal behaviour. Prof. Jennings has rescued the animalculæ from the bonds of automatism too hurriedly thrust on them, and has afforded a secure basis for the study of the evolution of intelligence. J. A. T.

MECHANISM, Mechanism. By Prof. S. Dunkerley. Pp. vi+408. (London: Longmans, Green and Co., 1905.) Price

98. net.

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WRITERS of text-books on mechanism have, of late years, been much influenced by the views of Realeaux on the classification of mechanisms, and the present work shows clearly the impress of these views; but the author has not hesitated to depart from the order in which Realeaux presented his theory of machines in order to suit the needs of beginners, who are apt to find the elaboration of the systematic theory somewhat dry if not accompanied by a wealth of illustration drawn from actual machines, even if these contain elements the properties of which have not been fully explained.

The author, as appears from his preface, is fully alive to the difficulties which the logical treatment of the subject presents, and he expressly states that his work is not intended to be a philosophical treatise on the subject.

From this standpoint the arrangement of the sub

The author has succeeded in writing a valuable text-book on mechanism which will repay a careful study by engineers and others who wish to obtain a knowledge of something more than the elements of this branch of science. E. G. C.

PRACTICAL ELECTROCHEMISTRY.

Perkin. Pp. x+322. (London: Longmans and
Co., 1905.) Price 6s, net.

ject-matter appears to be quite a proper one, for at the present time almost everyone is familiar with the elementary properties of gear-wheels, clutches, the mechanism of steam engines and the like, because of their increasing use in everyday life, and more especially of late, owing to their applications to selfpropelled vehicles. On the other hand their less obvious, although not less important, properties are possibly not so well understood; thus, to take a single Practical Methods of Electrochemistry. By F. Mollwo instance, the conditions to be satisfied in order to produce true rolling motion by gear wheels require a knowledge of the properties of various curves, and this latter subject may well be left to a later stage, as is done in the present work, although it need not prevent a study of machines containing gear wheels when this knowledge is not absolutely necessary for the purpose. The author has therefore described many machines using higher pairing quite early in the book, and has left the more detailed examination of some of the elements for later chapters; this adds very much to the general interest of the reader, while its drawbacks are small. The work opens with an introductory chapter in which the usual definitions occur relating to machines, kinematic chains, lower and higher pairs, and the like, and this is followed by a chapter which is exceedingly interesting on simple

machines and machine tools.

Chapters iii. and iv. deal chiefly with mechanisms of the quadric crank and double slider crank chain forms, all those possessing important geometrical properties being grouped together. Naturally the pantograph finds an important place here, and to amplify this section there are descriptions of the copying lathe and also a machine on the same principle for drilling square and hexagon holes. In a future edition it might be worth while to insert, in a suitable place, an account of the epicyclic trains which form an essential part of some machines for turning nuts and bolts to a practically perfect square or hexagon section.

The next two chapters deal with velocity and acceleration diagrams, and we are sure that all students of mechanism will feel greatly indebted to the author for the clear manner in which he has presented this part of the subject. The remainder of the book deals with gear wheels, non-circular wheels and cams, and these are discussed on the usual lines.

There is also a section devoted to gear-cutting machinery, which gives an interesting account of this special branch of machine tool work.

LECTROCHEMICAL methods, both of analysis and preparation, have in recent years undergone such rapid development, and have reached such a degree of importance, that systematic instruction in their employment has become an indispensable part of the training of the modern student of chemistry. This book, therefore, forms a welcome addition to the ordinary laboratory manuals.

After a general account of electrical magnitudes and units, measuring instruments, and electrolytic apparatus, the author gives practical instructions for electrochemical analysis. The conditions for the quantitative electrodeposition of the individual metals are first discussed; then follows a section on quantitative oxidation and reduction at the electrodes, and, finally, directions are given for the separation of

metals from mixed solutions of their salts. The last

and longest section of the book deals with preparative electrochemistry. The primary subdivision of the subject is into the preparation of inorganic and of organic compounds, the latter section being treated in three chapters on organic electrolysis, reduction of organic compounds, and oxidation of organic compounds respectively.

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The practical instructions are on the whole adequate and accurate, so that the student could acquire with little assistance a sufficient acquaintance with the working methods of electrochemistry. Whilst the book is satisfactory in this, the most important, feature, it shows in other respects many signs of hasty composition, which greatly detract from its value. For example, there are frequent evidences of haste in the treatment of electrical units. In the table on p. 9 the heading of the last column but one is "electrochemical equivalent per coulomb in mg. per sec."; the words "per sec." are not only superfluous but misleading. On p. 29 we find 'I kilowatt = 101.93 kilogrammeters,' and "I horsepower is 75 kilogrammeters," where the words "per second" should have been added in both cases. Nothing is more detrimental to clear thinking on the part of the student than slipshod statements of this kind. Again, in the table of "useful data" on p. 286 we find "I kilowatt = 1000 watt-hours," and volt x amperes = watts." Such data are the reverse of useful. A curious batch of mistakes is to be found on pp. 231–232. It is stated on p. 231 that the electroThe illustrations are mainly line drawings, exceed- lyte for the preparation of diethyl succinate is "acid ingly well adapted for descriptive purposes, and with potassium or sodium malonate" instead of "ethyl a few exceptions the photographs of machinery are potassium or sodium malonate." On the same page clear and distinct. A series of numerical examples at | we twice find “diethyl adipic acid" instead of diethyl the end of the book will be of much value to students. | adipate, and on the succeeding pages a similar error

It is somewhat remarkable that no place is found in the book for the consideration of so fundamental a subject as the degrees of freedom possessed by a body and the applications which follow from a recognition of these principles in geometrical slides and clamps, such as are described in Thomson and Tait's "Natural Philosophy." Ignorance of these fundamental principles has been one of the most fruitful causes of bad design in mechanism.

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is repeated. On pp. 226-227 it is surely wrong to ascribe the formation of the trace of ethylene found during the electrolysis of an acetate to the same cause as that which produces the plentiful yield of ethylene during the electrolysis of a propionate. The fact that equation v. is divisible by 2, and that equation iv. is not so divisible, is almost in itself sufficient evidence that the actions are of essentially different character. It is somewhat surprising to find that the kathodic reduction of nitrites, nitrates, and arsenical pounds finds treatment under the heading "Metals deposited as Oxides at the Anode" (pp. 145-150). These and similar slips are minor blemishes; but it is to be hoped that the author will subject his book to a thorough revision for their removal when a second edition is called for.

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The references to original papers are numerous, and a convenient table of five-figure logarithms, with instructions for its use, is contained in an appendix. The value of the table might be still further augmented by the inclusion of instructions for the use of the decadic complements of logarithms, a device of which the chemical student is almost invariably ignorant.

OUR BOOK SHELF.

Das Alter der wirtschaftlichen Kultur der Menschheit, ein Rückblick und ein Ausblick. By Ed. Hahn. Pp. xvi + 256. (Heidelberg: Carl Winter, 1905.) Price 6.40 marks.

In the opinion of Dr. Hahn, well known as the inquirer stages"-hunting, pastoral pursuits, agriculture-the mass of the reading public will not change its traditional views on pre-history and primitive culture unless the specialist is prepared to do more for it than issue specialist literature. With the object of making propaganda for his views on the domestication of animals, the forms of cultivation, the transition from hoe-cultivation to plough-cultivation, the invention of the plough, the use of the ox as draught-animal, the share of woman in primitive culture, and especially the development of personal property, Dr. Hahn has written the present work, and his object in so doing is commendable. Even specialist literature, however, is not above all considerations of form and logical sequence of ideas; in an oeuvre de vulgarisation it is a fortiori necessary that there should be an orderly development of facts and of the conclusions to be drawn from them; and this, unfortunately, Dr. Hahn has not given us. Not only is the book in places indigestibly full of facts the connection of which with the main argument is not always made clear, but too much is attempted; to the list of subjects given above must be added the description of the economic conditions and interrelations of China, Babylonia, India, and Egypt, a discussion of the origin of the wheel and the waggon, much polemical matter, dealing with criticisms which the public has never read, and finally excursuses on the fiscal question, socialism, and other subjects unconnected with his immediate purpose. It would be unfair to deny that the book is interesting and stimulating, but it is rather a causerie than an exposition of the author's theories. This is the more unfortunate because his views on the domestication of animals, the forms of cultivation, and the stages of economic evolution are largely accepted. From mere lack of literary skill Dr. Hahn will leave his readers comparatively

who revolutionised our ideas on the so-called "three

unmoved. As an example of the deficiencies of the book we may mention that the process of domestication of cattle is dismissed with a mention. Many of the author's theories are improbable; it is unnecessary to suppose that the curved horns imitating the shape of the crescent moon first led to the sacro-sanctity of cattle; there are animal cults everywhere. Personal property, even in vegetable food, was known before domesticated plants; the Australian natives store up We do not need to look to the bunya-bunya nuts. apparent motion of the stars for the explanation of the origin of Babylonian god-processions, which are a natural method of disseminating the holy influence. The connection of sexual ideas with agriculture may be secondary; syncretism is disregarded in this and other instances. It may not be out of place to say that a few maps of culture areas would have been very helpful, and not to the general reader only. Ń. W. T.

Infantile Mortality and Infants' Milk Depôts. By G. F. McCleary, M.D., D.P.H. Pp. xiv + 135(London: P. S. King and Son.) Price 6s, net. THE publication of the evidence before the InterDepartmental Committee on Physical Deterioration has directed general attention to such subjects as infant feeding. The decreasing birth rate and the appallingly high death rate among infants are dealt with by the author in the earlier chapters of his book.

It is

An increasing number of mothers are unable to nurse their children, so that some method of artificial feeding has to be adopted. The death rate in 1904 among children under one year was 146 per 1000 births, and even these figures by no means represent the total evil, for many of the survivors must be seriously affected. How can this fearful waste of life viz. the establishment of depôts worked by the be stopped? Dr. McCleary deals with one solution, municipality and partially rate-supported. generally agreed that cow's milk is the best substitute for human milk. Various opinions are held as to the degree of modification that may be necessary, but pure cow's milk is the basis from which to work. Even if a pure milk were on the market the poor could not afford to buy it. The question of State assistance arises. Dr. McCleary leaves the moral question as to whether it is for the ultimate good of a people to relieve them of their parental duties. Within the compass of 130 pages he wisely restricts himself to the practical working of the depôts, and his testimony is of interest. In France the milk as he speaks with knowledge of the Battersea depôt depôt system is carried out to a considerable extent, unmodified sterilised milk usually being supplied (Budin's method). In America the tendency is to follow Rotch in giving modified unsterilised milk. The author repeats the necessary warning that a dirty milk is not made clean by sterilisation, and from this it follows that no depôt is on a satisfactory basis unless it has absolute control of its own milk supply. Dr. McCleary advocates much more stringent supervision of the general milk supply, and the establishment of municipal depôts on the lines of that at Rochester, U.S.A.

The book is well illustrated.

A Critical Revision of the Genus Eucalyptus. By J. H. Maiden. Parts i. to v. Pp. iv+146. (Sydney: W. A. Gullick, 1903-4.)

THE classification of the Australian eucalypts presents similar difficulties to those which confront the botanist who undertakes the arrangement of the Hieracia or Rubi of our native flora, with the additional disadvantages that the eucalypts are trees or shrubs, and their distribution is more extensive. In the cir

cumstances it is natural that monographers should have expressed diverse opinions as to the limits of the species, and that different characters and parts of the plant should have been taken as a basis for classification. Bentham grouped the species according to the shape and mode of dehiscence of the anthers, and von Mueller followed his lead. Prof. Tate has proposed a system based upon the structure of the fruit, whilst of vegetative characters, the cotyledons, leaf-veins, stomata, gums, and timber have all been tested in the hope of finding satisfactory criteria. Mr. Maiden attaches considerable importance to the bark and timber for the guidance of the forester, but recognises that the anthers and fruit are the best Characters for the systematist.

In the present monograph the object of the author has been to include, with a description of the important characters, the substance of all recorded observations and investigations which might assist in determining the position and value of species or varieties. Synonyms are considered in detail, with the original description of each where it has been proposed as a species, and the range of each species is noted; finally, the author's views are crystallised in a discussion of the affinities of allied species. These views are based not only on the examination of specimens from important herbaria, but also upon much careful study of the growing trees in their native localities. Whilst recognising the desire of the author to render the work as comprehensive as possible, it must be said that its practical value would be increased by a considerable reduction in the amount of material, in the size of print and in the spacing. The five parts issued amount to 145 pages, and contain twenty-four plates for eight species, so that the complete work will be bulky and exclusive as to price. It may be suggested that a supplement to this treatise in the shape of a compendium suitable for foresters and students generally would be most useful. Hymenopteren-Studien. By W. A. Schulz. Pp. 147. (Leipzig: Engelmann; London: Williams and Norgate, 1905.) Price 4s. net.

THE present work consists of three essays, the first relating to African Hymenoptera (chiefly Vespidæ and Fossores), the second describing new genera and species of Trigonalidæ, and the third discussing Vespida and Apidæ from the Amazons. The work is chiefly descriptive, and will hardly appeal to any but specialists, who must of course consult it when working at the faunas and groups which are discussed in it.

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE. No notice is taken of anonymous communications.]

The High-frequency Electrical Treatment. THE inquest on a lady who died in the Charing Cross Hospital on April 11 must be of interest to those who employ the high-frequency electrical treatment. The report of the case in the Standard of April 17 is as follows:

On April 11 she (the deceased) was under treatment, lving on the electrical couch. Suddenly witness observed the perspiration break out on her face, and immediately stopped the current. He watched her for a while, and as she seemed to be in a collapsed state he administered a spoonful of sal volatile. Then he recognised symptoms which pointed to a serious state of affairs,' and sent for Dr. Bailey. The lady was removed to another ward and died in the evening. Death was caused by hemorrhage of the brain, following a rupture of an artery. This was not a consequence of the electrical treatment; she would

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Now that high-frequency electrical discharges are much employed in medical work, being the newest and most up-to-date method of treatment for many diseases, it is somewhat important that even "mere coincidences," such as that cited, should not be overlooked or treated lightly; it is only by collecting evidence on such points that any real knowledge respecting the action of the treatment can be obtained. Shortly after the experiments of N. Tesla on electrical discharges, I carried on many experiments on the subject, and from somewhat painful experience I have learned that one source of trouble may be overlooked by many, since it is a secondary action, so that while the utmost attention may be given to the behaviour of the discharge itself, but little may be given to the action of the air which has been subjected to an electrical discharge. The danger of breathing such air was pointed out by me long ago (NATURE, 1896), and by many other workers with electrical discharges since then. Air which had been acted on by the high-frequency discharge, when breathed, caused irritation to the throat and lungs, and a feeling of suffocation, in some cases very severe. This is rather to be expected, since ozone and ozonised air act on blood, albumen, and organic substances readily. Profs. Roscoe and Schorlemmer write thus in their treatise on "Chemistry," p. 243, vol. i. (subject, ozone) :-" Whilst blood is completely decolorised, the albumen being entirely, and the other organic matters being nearly all destroyed.")

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The trouble mentioned was removed to a considerable extent by inducing a strong draught of warm air across the chamber where the apparatus was used. I feel that I am taking a great liberty in suggesting anything to the high-frequency specialist, who will give me at once the " and reason why self-induction is expressed as a length, why a rapidly varying electromagnetic field causes flashes of light to be seen when the head is placed in such a field. I would suggest that in connection with the method of treatment with the high-frequency discharge, all evidence of new phenomena should be collected and sifted in a scientific spirit, whether it be for or against it.

Operators now take every possible precaution to guard themselves against the evil effects of the X-ray, which at first was treated as quite innocuous. May not the highfrequency discharge in a modified form have a somewhat similar kind of action, and should it not be treated with as much, or at least some, caution?

F. J. JERVIS-SMITH.

The Critical Temperature and Pressure of Living Substances.

It is well known that living substance is in a labile state, its constructive or destructive metabolism being determined by minute changes, sometimes of temperature or pressure, sometimes of other dynamic conditions. But Mr. Geoffrey Martin's suggestion (NATURE, April 27, p. 609) that the lability is due to the great number of atoms in the molecules of living substance, or to the complex "carbon compounds present, gives only a partial explanation.

The decomposition of a chemical compound under raised temperature, diminished pressure, &c., depends not only on the size and complexity of the molecules, but also on the tendency of the atoms to re-arrange themselves and form more stable compounds, generally with dissipation of energy. For instance, the paraffins with large molecules are fairly stable, the products of their decomposition being hydrocarbons still. Fatty acids with equally large molecules are less stable, for there is a tendency_to_split_off substances of higher oxidation, leaving a hydrocarbon residue. This tendency increases with the increase of oxygen in compounds, and so the small molecule of glucose is less stable than the large molecule of fatty acid. The presence of nitrogen is often a cause of instability, especially when the nitrogen forms a link between elements (or groups) of opposite polarity; and the instability is most marked when the nitrogen is combined with oxygen on the

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