NUTRITION. 
exists in a condition that can rightly be termed 
organised. Moreover, as it is clear that the 
gelatinous tissues may be formed at the ex- 
pense of albumen, we are justified in regard- 
ing this substance as the common pabulum 
forall. 
In order to form a definite conception of the 
nature of the transformations, which this prin- 
ciple is destined subsequently to undergo, it is 
important to bear in mind, in limine, that al- 
____ bumen cannot be regarded as possessed of any 
_ properties that characterize it as a vital com- 
_ pound—or, in other words, that essentially 
distinguish it from compounds of an ordinary 
chemical nature. In its coagulability by heat 
or by acids—in its combination with alkalies 
as an acid, or with acids as a base—and in the 
absence of any power of spontaneously passing 
_ into forms more decidedly organic than the 
granules which are seen when it is made to 
coagulate slowly—it is closely analogous to 
many substances which belong to the domain 
of inorganic chemistry. It appears, then, to be 
_ totally unpossessed of the property of plasticity ; 
_ by which we mean the power of being at once 
converted into organised tissue: so that any 
_ deposit, whether fluid or solid, which mainly 
hi consists of albuminous matter, must be regard- 
ed as aplastic. This is a principle of great 
importance, as we shall see further on. 
re albumen is ready to be appropriated 
_ by the tissues as the material for their nutri- 
tion, it must undergo a very important change— 
not so much, however, in its chemical compo- 
Sition, as in the re-arrangement of its particles 
in a new mode, by which its properties are es- 
Sentially changed. There seems reason to 
believe that, in the proportions of its ultimate 
elements, it is identical with the substance 
_ termed fibrin, into which it is changed during 
| its passage through the chyliferous and sangui- 
_ ferous vessels. [See Arpumen and Fisrin.] 
But there are such decided and well-marked 
ifferences between these two compounds, as 
' indicate that they fulfil entirely different pur- 
_ poses in the animal economy ; and that whilst, 
_ chemically speaking, they are isomeric, the 
_ fibrin is endowed with properties of a distinctly 
vital character—that is, altogether different 
_ from any with which mere chemistry brings 
_ US acquainted, One of the most obvious mani- 
2 of this difference is the property 
_ which is universally regarded as distinctive of 
fibrin—its tendency to coagulate spontaneously 
when withdrawn from the living vessels, and to 
_ pass into the form of a tisswe more or less 
' definitely organised. As will presently be 
_ shown, the completeness of this transformation 
my ds upon two circumstances in particu- 
i er perfect elaboration: of the fibrin it- 
self, and the vitality of the surface upon 
gwhich the concretion takes place. When the 
fibrin is highly elaborated, it will coagulate in 
the form of a definite network of minute fibrille, 
even upon a dead surface, as a slip of glass; 
| this is the case, for instance, with the fibrin of 
| the buffy coat of the blood, or with that of the 
| liquor sanguinis (coagulated lymph,) poured 
| out for the reparation of an injured part. But 
743 
in the ordinary fibrin of the blood, the fibrilla- 
tion is less distinct, when the concretion takes 
place upon a dead surface. When it occurs in 
contact with a living surface, however, the co- 
agulation takes place more gradually ; and it 
seems as if the particles, having more time to 
arrange themselves, become aggregated into 
more definite forms, so that a more regular 
tissue is produced—just as crystals are most 
perfectly formed, when the crystalline action 
takes place slowly. It was formerly imagined, 
that the muscular tissue is the only one pro- 
duced at the expense of the fibrin of the blood ; 
the other tissues being formed from its albumen. 
This, however, is unquestionably erroneous. 
There is no proof whatever, that albumen, as 
long as it remains in that condition, ever be- 
comes organised; whilst, on the other hand, 
there is abundant evidence that the plasticity 
of any fluid deposit—that is, its capability of 
being metamorphosed into organised tissue—is 
in direct relation with the quantity of fibrin 
which it contains. Thus the liquor sanguinis 
or coagulated lymph, thrown out for the repa- ~ 
ration of injuries, contains a large amount of 
fibrin ; and this substance is converted, not at 
first into muscular fibre, but (whatever may be 
the tissue to be ultimately produced in its 
place) into a fibrous network, which fills up the 
breach, and holds together the surrounding 
structure. This may be regarded as a simple 
form of areolar tissue, which gradually be- 
comes more perfectly organised by the exten- 
sion of vessels and nerves into its substance, 
and in which other forms of tissue may subse- 
quently make their appearance. This process 
will be more particularly described hereafter ; 
it is at present noticed here, as an illustration 
of the general fact, that fibrin is to be regarded 
as the plastic element of the nutritive fluids. 
The change from albumen to fibrin is, there- 
fore, the first important step in the process of 
assimilation. It commences in the absorbent 
system ; for the chyle is usually found to con- 
tain fibrin, even before it enters the mesenteric 
glands (as is indicated by its tendency, however 
feeble, to spontaneous coagulation) ; and after 
it has passed through them, the quantity of 
fibrin is considerably increased, so that chyle 
drawn from the thoracic duct usually coagulates 
with tolerable firmness. This process of elabora- 
tion continues in the blood: for the quantity 
of fibrin it contains is always kept up, in health,’ 
to a certain standard, although there must be a 
continual withdrawal of it for the nutritive pro- 
cesses, without a corresponding regular supply 
from the chyle ; and we find it, moreover, un- 
dergoing a sudden and remarkable increase, 
under the influence of local agencies. The 
question naturally suggests itself, therefore— 
what is the cause of this change? It has been 
usually attributed to some influence effected 
upon the albuminous fluid, by the living sur- 
faces over which it is passing; and the increase 
in the amount of fibrin in the chyle, which is 
specially noticed after its passage through the 
mesenteric glands, has been thought due to 
some peculiar action of the blood that may 
come into relation with it, through the thin walls 
