spores, animalcules, diatoms, desmids, cells and filaments of algæ, and spores of fungi. The only bodies which were of constant occurrence, and generally in great abundance, were small oblong cellules, which were either isolated or grouped in masses. They had a distinct nucleus contained within a smooth cellular envelope. He decided that they were algal cellules chiefly resembling palmellæ, and found that they only occurred in malarial districts.

He then proceeded to look for them in the air, his method of procedure being to suspend pieces of glass over marshy pools and swampy places. The glasses were set in the evening and removed before sunrise next morning. Drops of water were found adhering to their under surfaces and containing numerous cells of various kinds, but none resembling the peculiar palmelloid cellules previously alluded to. These were, however, constantly present in considerable numbers on the upper surfaces. His next step was to endeavour to ascertain from what source they were derived; and, after a considerable amount of fruitless search, he discovered it in a sort of greyish mould covering the recently exposed surfaces of cracks in rich prairie ground, which had been recently dried and was much broken up by the feet of cattle. On suspending glasses over places covered by this mould, he found numbers of the cellules in the fluid on their under surfaces.

In following out these experiments, Dr. Salisbury came to the conclusions that cryptogamic spores rise chiefly during the night and fall shortly after sunrise; that the height to which the cellules in question rose was 30 to 100 feet from the surface; that none of them were present during the day; that covering the soil to a depth of several inches with straw or quicklime prevented their rise; that a stay of fifteen minutes in places in which they abounded gave rise to dryness and febrile heat of the throat coincident with their presence in the pharyngeal mucus; and that persons exposed to their inhalation, even far from their original source, under entirely different circumstances, in non-malarial districts, suffered from attacks of fever as a consequence.

We hardly think that there could be more convincing evidence than this. But then it has to be borne in mind that the district under examination was somewhat an exceptional one.

The observations of Dr. Swayne and Mr. Brittan, though they were called in question by the subsequent Report of the Royal College of Physicians, similarly give evidence in favour of this view of the matter. They go to show that in cholera times there exist in the atmosphere peculiar cells, whose structure, as far as they could see, was identical with that of the well-known annular cells from choleraic fæcal discharges. They

went so far as to publish figures of these cells, which they alleged were absent from localities which had no cholera cases in their neighbourhood. Dr. Ransome, again, gives his testimony in favour of the view that the air we breathe contains numerous organisms. In a paper read before the Philosophical Society of Manchester, in the year 1870 (and reported in these pages), he stated that an examination of the air showed that in cases of diphtheria numerous greenish conferval filaments appeared; and in the air collected from the neighbourhood of cases of measles, whooping-cough, and phthisis abundant examples of small round confervoid cells were found. At the same meeting at which the above statement was made, Dr. H. Browne alleged that he had obtained nearly the same results.

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Beside these, there are several others on the same side. Signor Selmi, of Mantua, states that he has examined the moisture proceeding from the air of marshes, and found that it consisted in a considerable proportion of spores of algae and active infusoria. Again, another observer, Dr. Balestra, has made important observations on the air in the Pontine marshes of Rome; and he states that there are in it the spores, of a greenish yellow colour and mm. in diameter, of a minute species of algae, and that these, he has no doubt, are the cause of those numerous cases of intermittent fever which are almost characteristic of the locality. M. Reveil also shows that the air in the wards of the St. Louis Hospital was, when collected by the microscope, abundantly charged with epithelial cells and various organic corpuscles. Evidence in favour of this view is also given by M. V. Poulet, who states ("Comptes Rendus," vol. lxv.) that he has found abundant quantities of Bacterium termo, Monas termo, and B. bacillus, in the air which had been breathed by persons who were suffering from common whooping-cough.

The annual Reports from the Army Medical Department, too, give us a good deal of evidence; and it is the more valuable, not from the fact of its leaning to one side more than another, as from the circumstance that the investigations recorded have been invariably conducted with that strict regard for truth which renders them valuable as impartial accounts. The statements vary a little, according to the observer that makes them, but some of them point distinctly to the fact that the air is decidedly impure from the nature of its contents. For instance, Dr. de Chaumont states that 120 cubic feet of air were found to contain "epithelium in large quantity, hair and various fibres, sand, soot, crystalline sub

"Sanitary and Medical Reports of the Army Medical Department

for 1867."

stances, and sporangia of fungi and monads in considerable quantity." Mr. Dancer's* researches on the air of Manchester are also of great interest, more especially as he gives an estimate of the amount of spores present in the specimens of air examined. He says that there were in 2,495 litres of the atmosphere (an amount that would be breathed by any ordinary individual in about ten hours) no less than 37,500,000 spores, exclusive of other materials. And besides those whose researches we have mentioned, there are many others whose inquiries all point in the same direction.

But it must be confessed that the opposite side is, in regard to the absence of spores originating epidemic diseases, not devoid of evidence also. It can name no less authorities than Ehrenberg, the greatest infusorial investigator in the world; Pouchet, the celebrated supporter of the well-known doctrine of spontaneous generation; the Royal College of Physicians; and MM. Joly and Musset; besides various other less celebrated authorities. But the first can only be cited as opposed to the idea that there are the germs of infectious diseases in the atmosphere; for he shows most conclusively, by infinitely the most extensive of researches, that the air contains an amount of animal life that is something extraordinary. But, says Dr. Cunningham,† when speaking on this part of the subject, "no special forms of infusoria or spores were to be found in the atmospheric dust during the epidemic of cholera in 1848." So we may almost count Ehrenberg on the other side, i.e. among the anti-contagionists. In point of fact the only men of great reputation upon this side are MM. Pouchet, Joly, and Musset. Their researches are really most remarkable, for they seem to have observed none whatever of the hosts seen by numerous other workers. Of course they did find (more especially Pouchet) some corpuscles and a few other organisms, but nothing at all to account for the multitude that were developed in water exposed to the air.

Now we must remember that these three (Pouchet, Joly, and Musset) were the special advocates of spontaneous generation, and that therefore they could not be expected to find an ample supply of animal and vegetable life already existing in the atmosphere. But it may be said we have no right to accuse them of falsity, and therefore we declare that we do not do so; but what we do say is, that persons who were engaged in a desperate argument against the existence of these germs in the atmosphere, were not the most likely persons to find them in that position.

They were published in the "Proceedings of the Literary and Philosophical Society of Manchester."

+ "Microscopic Examinations of Air," 1874.

At all events, such is the evidence pro and con. We have a great deal of valuable testimony in favour of the existence of animal and vegetable life in the atmosphere, and a certain proportion of that testimony goes to show that contagious and infectious diseases may have their origin in atmospheric causes; whilst, on the other hand, we have hardly a tenth part of witnesses in favour of the view that the atmosphere is not a centre of animal and vegetable life, and that diseases do not spread through the assistance of atmospheric germs. We are now in a position to examine the latest evidence that has been offered on the subject, and to raise one or two objections that the whole method of investigation seems to us to be liable to.

We must now examine Dr. Cunningham's labours. These appear to us to be most valuable, and he has published them in a form which, for completeness of detail, for skilful arrangement, and for excellence and number of illustrations, has certainly no equal, at least in our language. Of course the reader must be referred to the work itself for the minute accounts. We can do little more than sketch in a most imperfect manner some of the results at which he has arrived. One of the first experiments he describes is of interest, as it shows how many different series of animal forms may arise in succession in the very same specimen of water which has been at first obtained from rain collected at a considerable height above the ground (having taken every precaution against uncleanliness), and which has been kept for several days perfectly free from the admission of the external air. In one specimen (No. II. p. 42 of Dr. Cunningham's work) the author found, seventy-two hours after it had been sealed, an ample amount of mycelial elements. Then two days subsequently (the specimens being regularly sealed after examination) he found an abundance of conidia. It was then sealed again, left for six days more, with the following results (see fig. 2, Plate CIX.):-" The filaments were then greatly disintegrated, but the cysts remained very distinct, and were present in abundance. They contained a mass of protoplasm marked with one or two granules and clear spaces, the latter of which could be seen to alter in number and position. In several instances these protoplasmic bodies were observed gradually to work their way out of their cysts, which were then left behind as extremely delicate rings, hardly visible save with careful examination. The process was comparatively slow, and the escaping zoospores, for such they seemed to be, showed a well-developed flagellum in active motion for some time before they were entirely free. Once detached in the fluid they moved actively about by means of the flagellum as well as by free amoeboid extensions of their substance, and in many cases the flagellum temporally or permanently disappeared, so that, had

the process not been actually observed to take place, the two conditions might have been regarded as belonging to distinct organisms. In other parts of the preparation, the mycelial threads had resolved themselves into innumerable conidial cells, while in others they were more or less completely decomposed into gelatinous masses containing granules and bacteroid staves."

Several other experiments of a similar kind were made, with pretty nearly the same results. The only question which here occurs to the author is that concerning the origin of bacteria; but that I think he gets over very fairly. The conclusions which he states are as follows:-1. Specimens of rain-water in Calcutta, collected with every precaution to ensure their freedom from contact contamination, sooner or later frequently show the presence of spores, mycelium, zoospores, monads, bacteroid bodies, and distinct bacteria. 2. They do not, as a rule, contain any of the higher forms of infusoria. 3. The zoospores are demonstrably derived from the mycelium arising from common atmospheric spores. 4. There is every probability that the monads and bacteria have a similar origin, but it remains quite uncertain whether their development is due to heterogenesis, or to the presence of their germs within their parent cells, or as the result of a process of normal development in the latter.

The next subject examined by Dr. Cunningham is that relating to the microscopic character of the air in sewers. He placed his aeroscope in such a position that it would have an opportunity of examining the air proceeding from the sewage of Calcutta, but the results he obtained were not very important (see fig. 3, Plate CIX.). He found as a rule nothing but bacteria and the spores, most probably, of aspergillus. And both these he thus accounts for. The bacteria, he says, are found here more readily than in the outer air, because the moisture renders them more readily seen; inasmuch as they change their form under the influence of drought, they are less observed in ordinary preparations. As to the presence of aspergillus, and that alone, he thinks it is due to the fact that of course other fungal spores could not exist in the sewer atmosphere, while aspergillus meets there the damp atmosphere and luxuriant organic matter which it requires.

The other specimens figured in our plate are copies of some few of those which Dr. Cunningham has collected by his aeroscope, which was exposed for 24 hours each day during the months of April, May, and June, 1872, at the Presidency Jail, and at a similar locality in Alipore. The results of these gatherings are not so strikingly remarkable as we should have expected, possibly for a reason that we shall refer to further on;