In one of these spindle-shaped or fibre-cells it is difficult to distinguish anything particular. In very large cells of this kind, and with a high magnifying power, we can certainly frequently distinguish a fine longitudinal striation (Fig. 5, 6), so that it looks as if here, too, fibrils of some sort were disposed lengthways in the interior, whilst ordinarily no trace of any transverse striæ is perceptible. Yet the pale, smooth muscles exhibit, chemically speaking, a pretty close agreement with the transversely striped ones, since a similar substance (the so-called Syntonin of Lehmann) can, by the help of diluted hydrochloric acid, be extracted from both; and one of the most characteristic substances which is met with in red muscles, namely Creatine, is met with also, according to the investigations of G. Siegmund, in the smooth muscular fibres of the uterus.

One of the preparations of red muscle which I have placed before you exhibits an appearance which is also pathologically interesting; among the fasciculi, namely, is one which presents the condition of the so-called progressive (fatty) atrophy. The degenerated fasciculus is smaller and narrower, and at the same time little fat-globules are seen arranged in rows between the longitudinal fibrils (Fig. 23, d). Atrophy in muscles is chiefly characterized by a diminution in the diameter of the primitive fasciculi affected; in fatty atrophy the more palpable change is added, that little rows of fat-globules appear in the interior of the primitive fasciculus, during the accumulation of which the proper contractile substance decreases in bulk. The more fat there is, the less contractile substance; or, in other words, the muscle becomes less capable of performing its functions in proportion as the normal contents of its fibres diminish. Pathological experience, therefore, also designates as the seat of the contractile power a definite substance, the occurrence of which, as especially the important investigations of Kölliker have taught us, is connected with certain histo

logical elements. Whilst formerly many other things besides the substance of muscle, as, for example, certain forms of connective tissue, were assumed to be contractile, lately the whole theory of contractility in the human body has been withdrawn within the limits of that substance, and observers have succeeded in tracing back nearly all the peculiar phenomena of motion to the existence of minute parts of a really muscular nature. Thus, in the human skin there lie little muscles about as large as the smallest fasciculi in the parietes of the urinary bladder, bundles consisting of diminutive fibre-cells, which run from the base of the hair-follicles towards the surface of the skin, and, when they contract, approximate the two. The result of this is naturally that the skin becomes uneven, and we get what is called a goose-skin. This singular phenomenon, which was previously regarded as inexplicable, has been simply explained by the demonstration of these purely microscopical muscles, the arrectores pilorum.

So also we now know that the greater part of the muscular layers in vessels is composed of elements of this kind, and that the phenomena of contraction exhibited by the vessels must be referred solely and exclusively to the action of muscular fibres, which are contained in them in the form of circular or longitudinal layers. A small vein or a small artery can contract only in proportion to the quantity of muscle with which it is provided, and they are only distinguished by the circumstance that either the longitudinal or the transverse muscular layers are the more strongly developed.

I have called your attention to this point because you can see from it, how a simple anatomical discovery may supply the most important information with regard to physiological facts, which are widely separated from one another, and how the demonstration of definite morphological elements may at once most essentially contribute to

the elucidation of functions, which, without any such data, would be utterly incomprehensible.

1 will omit to speak here of the more intimate structure of the nervous system, because I shall have occasion hereafter to consider it in a more connected form, else this would be the subject which would most suitably come next, seeing that there exist many points of resemblance in the structure of muscular and nerve-fibres. But in the nervous system we find, in addition, nerve-cells (Ganglienzellen), which connect the individual fibres with one another, and must be regarded as the most important storehouses for all nervous energy.

FIG. 26.
A

Concerning the structure of the vascular system also I

Fig. 26. Small artery from the base of the cerebrum after the application of acetic acid. 4. Small trunk; B and C, larger branches; D and E, branches of the smallest size (capillary arteries). a, a. External coat, with nuclei, which run in the direction of the length of the vessel, and are seen first in a double and afterwards in a single layer, with a striated basis-substance; at D and E

will not here treat in detail, but will only say as much as is necessary to give a cursory view of the matter.

A capillary vessel is a simple tube (Fig. 3, c), in which we have, with the aid of our present appliances, hitherto only been able to discover a simple membrane, beset at intervals with flattened nuclei, which, when seen in the middle of the surface of the vessel, present the same appearance as in the elements of muscle, only that they usually lie more at the sides, and therefore frequently have an awl-shaped appearance, from their sharp border alone being perceived. It is this, the most simple class of vessels, which we now a days solely and exclusively call capillaries, and with regard to them we cannot say that they become wider or narrower by means of any action of their own, but at most that their elasticity renders a certain degree of contraction possible. Nowhere are there to be witnessed in them genuine processes of contraction or relaxation succeeding it. The discussions which formerly took place with regard to the contractility of the capillaries really had reference to small arteries and veins, the calibre of which grows narrower through the contraction of their muscular coats, or wider upon the occurrence of relaxation in consequence of the pressure of the blood. This is one of the first facts, and an important one it is, which have resulted from the more accurate histological knowledge of the smaller and larger vessels, and it shows us that we cannot speak of the general properties of vessels, inasmuch as the capillaries differ essentially in structure from the small arteries and veins. These are composite structures, partaking of the nature of organs, whilst a capillary vessel is rather a simple histological element.

the coat is reduced to a single layer, with longitudinal nuclei, which here and there have been replaced by masses of fat-granules (fatty degeneration). b, b. Middle coat (circular fibrous, or muscular, coat), with long, cylindrical nuclei, which run transversely around the vessel, and at its borders (where they look as though they had been cut across) present the appearance of round bodies; at D and E transverse nuclei of the middle coat becoming continually scarcer. e, c. Internal coat, at D and E with longitudinal nuclei. 300 diameters.

Now that we have, gentlemen, completed a very general survey of the physiological tissues, the question arises, how the pathological ones in their turn comport themselves. By pathological tissues, of course, those only can be meant which really constitute pathological new formations, and not physiological parts which have simply undergone alteration in consequence of some deviation from the normal processes of nutrition. We have in them to deal with genuine neoplasms, with the additional matter furnished by the growth of new tissues in the course of pathological processes, and the question is, whether the general types which we have established for the physiological tissues will also be found to hold good in the case of the pathological ones. To this I unreservedly reply, yes; and however much I herein differ from many of my living contemporaries, however positively the peculiar (specific) nature of many pathological tissues has been insisted upon during the last few years, I will nevertheless endeavour in the course of these lectures to furnish you with proofs that every pathological structure has a physiological prototype, and that no form of morbid growth arises which cannot in its elements be traced back to some model which had previously maintained an independent existence in the economy.

The classification of pathological new formations, of genuine neoplasms, was formerly by most observers attempted to be based upon their different degrees of vascularity. If you examine the different treatises which appeared upon this subject up to the time of the cell-theory, you will find that the question of organization was always decided by that of vascularity. tained vessels was regarded as part as unorganized which was But this, according to present notions, is an incorrect view of the matter, inasmuch as we have also physiological tissues without vessels, as for example, cartilage.

Every part which conorganized, and every destitute of vessels.