34

Inflammatory Crust of the Blood.

the floor, and a few drachms more of blood were taken into a fourth cup.

Of these four quantities of blood, that which was taken away the last was coagulated in three minutes; that first taken was coagulated in twelve; that taken in the second cup was not completely coagulated in twenty-two minutes; neither of the three had an inflammatory crust. But the blood received into the third cup began in five minutes to appear transparent on its surface, was not completely coagulated for thirty-five minutes, and exhibited a remarkably thick and tough size*.

x Hewson, 1. c.

CHAPTER III.

OF MUSCULAR ACTION.

VARIOUS textures in living bodies are observed to exist at successive periods in two different states, to be at one moment elongated, at another shortened. The change from the one state to the other is the beginning of motion. The phenomena of each case, in which motion is thus produced, have common points enough to authorize us in ascribing the whole to one property, which has. been termed Irritability. They are broadly distinguished from the effects of elasticity, of gravity, from the expansions and contractions of bodies, which are caused by changes of temperature; and although they in some respects correspond with the results of galvanic agency, yet the analogy seems far too loose and incomplete to warrant a conjecture that the movements of irritable parts depend upon a modification of the electric principle.

The parts of the human frame which possess irritability are, muscular substance, the substance of the uterus, the fibrous coat of arteries, the unattached margin of the iris, some parts of the skin, and perhaps the dense texture which is employed in forming excretory tubes. In the phenomena of muscular action alone, which form the subject of the present chapter, a surprising diversity exists.

Muscular substance is what is commonly called flesh in animals; varying in different genera and species, in

36

Appearance and Composition of Muscles.

different individuals of the same species, in different parts of the same body, both in firmness and colour, it uniformly preserves a more essential point of resemblance in its fibrous structure. Yet it may be remarked, that the firmness and depth of colour of muscles, taken relatively, are generally proportionate to the frequency and energy with which they have been used.

The flesh of the human frame is of a reddish brown colour in the muscles of the trunk, head, and limbs, and in the heart; of a pale gray in the muscular coat of the alimentary canal and of the bladder. But upon maceration in water it is found in each case to be reduced to little more than a colourless fibrin. The water that has been employed contains albumen, gelatine, extractive matter, and various salts. Perhaps the most remarkable circumstance, which chemistry has ascertained in this investigation, is that nitrogen exists in larger proportion in the muscles of animals with red blood, which possess the greatest variety of function, and enjoy them in the most perfect state, than in those of fish or reptiles; and that in animals of the same species, those of adult age contain more nitrogen than the same muscles soon after birth. In young animals, it appears that the muscles as well as the membranes and bones contain a considerable quantity of gelatine; but as they advance in age the gelatine disappears, and is replaced by albumen. Fat, or oil contained in delicate membranous cells, is found in the substance of muscles, more coarsely wrought into the texture of some than of others, and in age than in youth.

a

Bostock's Elementary System of Physiology, vol. i. p. 152.

Mode of Displaying the Primary Filament. 37

When a portion of a muscle is examined, it appears to consist of flattened bands, or lacerti, of a soft yielding flesh, connected together by a thin elastic transparent membrane. Each of these bands admits of separation into slender strips or fibres, which again may be resolved into others yet finer. All the fibres are individually invested and joined together by processes of the same membrane, which unites the lacerti.

A few hours after death the membrane investing muscles is found to be firmer and more adherent than at a later period. When decomposition commences, a moisture is produced between the membrane and the flesh, probably through the resolution of the finer productions of the membrane. If in this state a lacertus be laid upon a piece of glass and be partially drawn asunder into shreds under a drop of water, fine fibres of different sizes are visible every where to the naked eye. If the portion spread out to the greatest tenuity be examined in a microscope, the fibres at one part or another are distinctly seen to consist of numerous minute threads of an uniform size. As these threads appear to admit of no further subdivision, it is presumable that they constitute the primary filaments of muscular substance.

In order to obtain a coarse measurement of the diameter of these filaments, thin streaks of blood may be drawn at random across the prepared surface; and it cannot fail of happening that at one point or another the globules of the blood will be so intermingled with the isolated filaments, that their relative breadth may be compared. The diameter of a globule of the blood appears to be nearly the same with the breadth of the primary filament of a muscle.

38

Nature of the Primary Filament.

If the primary filaments be now viewed under a varied light, by altering the inclination of the mirror attached to the microscope, or by shading the light with the hand, another circumstance becomes apparent at one point or another of the surface: the filament, instead of presenting a perfectly even outline, is seen to be regularly indented, and faint cross shadows upon its surface, more or less clearly distinguishable, show that it consists of cohering sphericles, which are nearly equal in size to those of the blood.

By the preceding method it is easy to obtain an approximation to the relative size of the muscular globules and of those of the blood, the discovery of which we owe to Sir Everard Home and Mr. Bauer.

The accurate observations of Mr. Bauer have determined that the size of the muscular globule exactly corresponds with that of the uncoloured globule of the blood; and that the primary filament consists of a series of such globules connected by an elastic medium, which admits of sufficient elongation that a visible interval may be produced between the globules".

It appears that in each fibre the primary filaments extend individually its whole length, and are laid parallel to each other. In different muscular parts the fibres are disposed in various ways, either parallel to each other, or convergent, or interwoven with and decussating each other.

Muscular parts receive a large supply of blood; but there is reason to believe that the distribution of the vessels is not so minute as former theories of nutrition sup

b Phil. Trans. vol. cxvi. p. 5.