742 
tion is required, for the maintenance of 
their normal texture and properties; but its 
amount will vary, according to the demand 
created by previous activity, and the conse- 
quent decay. ‘ 
The materials required for the nutrition of 
the tissues of the animal body seem to be sup- 
plied, for the most part at least, in forms pos- 
sessing a similar chemical composition, by the 
vegetablekingdom. It will be presently shown 
that albumen may be regarded as the pabulum, 
at the expease of which all the organised tex- 
tures (properly so called) of the animal fabric 
may be constructed. The really-organised part 
of this fabric, indeed, appears open to de- 
widely from the protein type of composi- 
Rou, Thus in fat, the areata by 
contained within cells, whose kl: ee com- 
posed of a protein principle ; and in the ner- 
vous tissue, re is Gectanblar that the walls of the 
cells and tubes are composed of an albuminous 
compound, though their interior is occupied by 
a substance of a character much more nearly 
approaching that of fat. Even with respect to 
the gelatinous tissues, as they are termed, 
there is much doubt to what extent they con- 
tain gelatin in their normal state; for where 
this can only be extracted from them by long 
boiling, it is not improbable that an actual con- 
version takes place ; since we know that pure 
fibrin may be converted, by long boiling, 
(which occasions the liberation of ammonia,) 
into a compound resembling gelatin in many 
respects. And in those which are most purely 
gelatinous, it is doubtful how far the gelatin is 
itself organized. The writer has lately ex- 
amined the sound of a cod with great care, both 
before and after the action of hot water upon 
it, and is satisfied that the gelatinous portion 
of it exhibits nothing that can be properly 
called organization—the only distinct appear- 
ances of fibres, cells, &c., being presented by 
portions which were left undissolved by the hot 
water, and which were, therefore, to be regarded 
as more allied to albumen than to gelatin in 
their composition. Similar remarks may be 
made in regard to the horny substance de 
sited in certain tissues; and it may roti 
be stated as a general theorem, that whilst in 
the plant, the materials which it derives from 
the elements around are combined and elabo- 
rated into non-azotized compounds for the pro- 
duction of organized tissue, and into azotized 
roducts for deposition in its cavities, these 
ast alone form the materials of the animal or- 
ganism, any non-azotized substances contained 
in it being inorganic in their condition. 
In considering the various stages of the nu- 
tritive process in animals, we shall do well to 
bear constantly in mind the leading facts in re- 
gard to the same process in the simplest cellu- 
plant: for we shall find that the elementary 
parts of the most complex animal organism go 
through a series of changes essentially the same ; 
so that the type of the function is everywhere 
. uniform, notwithstanding the vast apparent dif- 
ferences in the mode in which it is performed. 
The cell of the red snow or yeast plant, for 
instance, is developed from an almost imper- 
NUTRITION. 
ceptible germ, by its own power of attracting 
to itself certain nutritive materials in its neigh-° _ 
bourhood, which it combines into the new 
forms required both for its own growth and in- 
crease, for the elaboration of certain peculiar 
matters contained in its cavity, and for the 
duction of the germs of new cells; and these, 
being liberated in time by the death of their — 
parent, go through, in their turn, the same series — 
of changes. We shall now trace these changes — 
in the highest and most ee form in 2 5 
they are presented to us ;—that is, as they oc-— 
cur in man, or any vertebrated animal. ss 
Elaboration of organizable materials —The 
alimentary substances taken in by the absorbent 
vessels uire to unde important — 
changes within the body, before they can b 
oer to the nutrition of its structure. Th 
chief constituents of the chyle, as at first al 
sorbed, are albumen and fat; the former is” 
destined to be converted into the material of 
the solid tissues ; the latter is chiefly designed 
for the maintenance of the animal temperature, 
by the combination it is made to undergo with 
the oxygen introduced through the lungs. 
is questionable, as already explained, wheth 
fatty matter, or any other non-azotized com 
pound, can ever be applied to the ' 
the animal body. Even if it should 
proved to be subservient to the 
of the azotized tissues, there can be no dou 
that it must have been first converted into a 
albuminous compound—that is, into some m 
dification of protein; and as the evidence h 
such a transformation ever takes place is | 
from being satisfactory, we have as yet node 
for examining the mode in which it is effect 
We shall, therefore, consider albumen as 
starting-point of the animal tissues, and sh 
endeavour to trace, so far as the present stati 
our knowledge admits, the processes by 
this is converted into the organized fabric. — 
In this assumption we seem justified by | 
very obvious considerations. First, in the | 
of a bird, (or any other oviparous animal,) 
find that, putting aside the fatty, matter o 
yolk, albumen is the sole organic compout 
the expense of which all its tissues are | 
formed ; so that, by the wonderful proe 
chemical and vital transformation, whic 
poe during the period of incubation, 
umen which it contained at first is 
morphosed into bone, cartilage, nerve, mi 
tendon, ligament, membrane, areolar t 
gelatinous matter, horny substance, fe: 
&e.,&c. Secondly, a similar metamo 
appears to be continually taking place” 
body of the adult animal; for every” 
compound employed as food appears to 
duced to the form of albumen in the di 
process ; so that this becomes the essentia 
stituent of whatever fluid is absorbed ~ 
nutrition of the tissues, It is true that 
taken in as food, may be absorbed and ¢2 
into the current of the circulation ; but) 
no doubt that it is altogether incapable of | 
applied to the re-construction of any b 
gelatinous tissues; and, as already st 
seems questionable whether, even in th 
be ev 
p-construc 
we! 
