DIGESTION. 
6857 times its own weight; and yet, in all 
probability, its weight was not much dimi- 
nished. 
\Y hat the substance is which possesses this 
coagulating property, has not yet been as- 
certained ; but it is evidently not very soluble 
in water : for the inside of a calf’s stomach, 
after being steeped in water for six hours, and 
then well washed with water, still furnishes 
a liquor on infusion which coagulates milk : 
and Dr. Young found that a piece of the 
inner coat of the stomach, after being pre- 
viously washed with water, and then with a 
diluted solution of carbonat of potass, still 
afforded a liquid which coagulated milk and 
Serum. 
It is evident, from these facts, that this 
coagulating substance, whatever it is, acts 
very powerfully ; and that it is scarcely pos- 
sible to separate it completely from the 
stomach. But we know at present too little 
of the nature of coagulation to be able to 
draw any inference from these facts. An 
almost imperceptible quantity of some sub- 
stances seems to be sufficient to coagulate 
milk: for Mr. Vaillant mentions in his 
Travels in Africa, that a porcelain dish which 
he procured, and which had lain for some 
years at the bottom of the sea, possessed, in 
consequence, the property of coagulating 
milk when put into it ; yet it communicated 
no taste to the milk, and did not differ in 
appearance from other cups. 
It is probable that the saliva is of service 
in the conversion of food into chyme as well 
as the gastric juice. It evidently serves to 
dilute the food ; and probably it may be 
serviceable also by communicating oxygen. 
The chyme, thus formed, passes from the 
stomach into the intestines, where it is sub- 
jected t o new changes, and at last convert- 
ed into two very different substances, chyle 
and excrementitious matter. 
The chyle is a white-coloured liquid, very 
much resembling milk. It is exceedingly 
difficult to collect it in any considerable 
quantity, and for that reason it has never been 
accurately analysed. We know only in ge- 
neral that it resembles milk ; containing, like 
it, an albuminous part capable of being co- 
agulated, a serum, and globules which have 
a resemblance to cream. It contains also 
different salts ; and, according to some, a 
substance scarcely differing from the sugar 
of milk. 
Concerning the process by which chyle is 
formed from chyme, scarcely any tiling is 
known. It does not appear that the chyle 
is precisely the same in all animals; "for 
those which are herbivorous have a greater 
length of intestine than those which are 
carnivorous. It is certain that the forma- 
tion of the chyle is effected by a chemical 
change, although we cannot say precisely 
what that change, is, or what the agents are 
by which it is produced. But that the change 
is chemical, is evident, because the chyle 
h entirely different, both in its properties 
and appearance, from the chyme. The 
chyme, by the action of the intestines, is se- 
parated into two parts, chyle and excre- 
ment : the first of which is absorbed by a 
number of small vessels called lacteals ; the 
second is pushed along the intestinal canal 
ami at last thrown out of the body altogether. 
After the chyme has been converted into 
chyle and excrement, although these two 
substances remain mixed together, it does 
not appear that they are able to decompose 
each other; for persons have been known 
seldom or never to emit any excrementitious 
matter per anum for years. In these, not 
only the chyle, but the excrementitious mat- 
ter also, w as absorbed by the lacteals ; and 
the excrement was afterwards thrown out of 
the body by other outlets, particularly by 
the skin: in consequence of which, those 
persons have constantly that particular odour 
about them which distinguishes excrement. 
Now in these persons it is evident that the 
chyle and excrement, though mixed toge- 
ther, and even absorbed together, did not 
act on each other; because these persons 
have been known to enjoy good health for 
years, which could not have been the case 
had the chyle been destroyed. 
It has been supposed by some that the 
decomposition of the chyme, and the forma- 
tion of chyle, are produced by the agency of 
the bile, which is poured out abundantlv, 
and mixed with the chyme, soon after its 
entrance into the intestines. If this theory 
was true, no chyle could be formed when- 
ever any accident prevented the bile from 
passing into the intestinal canal: but this is 
obviously not the case ; for frequent instan- 
ces have occurred of persons labouring under 
jaundice from the bile-ducts being stopped, 
either by gall-stones or some other cause, 
so completely, that no bile could pass into 
the intestines; yet these persons have lived 
for a considerable time in that state. Con- 
sequently digestion, and therefore the form- 
ation ot chyle, must be possible, independ- 
ant of bile. 
The principal use of the bile seems to be 
to separate the excrement from the chyle, 
after both have been formed, and to produce 
the evacuation of the excrement out of the 
body. It is probable that these substances 
would remain mixed together, and that they 
would perhaps even be partly absorbed to- 
gether, was it not for the bile, which seems 
to combine with the excrement, and by this 
combination to facilitate its separation from 
the chyle, and thus to prevent its absorp- 
tion. Eourcroy supposes that the bile, as 
soon as it is mixed with the contents of the 
intestinal canal, suffers a decomposition ; 
that its alkali and saline ingredients combine 
with the chyle, and render it more .liquid, 
while its albumen and i'esin combine with 
the excrementitious matter, and gradually 
render them less and less fluid ; and this 
theory is certainly very probable. The bile 
also stimulates the intestinal canal, and causes 
it to evacuate its contents sooner than it 
otherwise would do ; for when there is a de- 
ficiency of bile, the body is constantly cos- 
tive. 
The excrementitious matter, then, which 
is evacuated per anum, consists of all that 
part of the food and chyme which was not 
converted into chyle ; entirely altered, how- 
ever, from its original state, partly by the 
decomposition which it underwent in the 
stomach and intestines, and partly by its 
combination with the resin and albumen of 
the bile. Accordingly we find in it many 
substances which did not exist at all in the 
food. Thus in the dung of cows and horses 
there is found a very considerable quantity 
of benzoic acid. The excrements of animals 
4. 
! have not yet been subjected to an accurate 
analysis, though such an analysis would 
throw much light upon the nature of di- 
gestion : for if we knew accurately the sub- 
stances which were taken into the body as 
food, and all the new substances which were 
formed by digestion ; that is to say, the 
component parts of chyle and of excrement, 
and the variation which different kinds of 
food produce in the excrement; it would be 
a very considerable step towards ascertaining 
precisely the changes produced on food by 
digestion. 
Vauquelin has ascertained that the faeces 
are constantly acid, always reddening vege- 
table blues. They run very quickly into 
fermentation, becoming at first more acid, 
but very soon begin to exhale ammonia. 
Pigeon-dung contains an acid of a peculiar 
nature, which increases when the matter is 
diluted with water ; but gradually gives 
place to ammonia, which is at last exhaled in 
abundance. 
To the same excellent chemist we are in- 
debted for an analysis of the fixed parts of the 
excrements of fowls, and a comparison of 
them with the fixed parts of the food ; from 
which some very curious consequences may 
be deduced. 
He found that a hen devoured in ten 
days 11111.843 grains troy of oais. These 
contained 
136.509 gr. of phosphat of lime 
219.548 silica. 
356.057 
During these ten days she laid four eggs ; 
the shells of which contained 98.776 gr. 
phosphat of lime, and 453.417 gr. carbonat 
of lime. The excrements emitted during 
these ten days contained 175.529 gr. phos- 
phat of lime, 58.494 gr. of carbonat of lime, 
and 185.266 gr. ot silica. Consequently the 
fixed parts thrown out of the system during, 
these ten days amounted to 
274.305 gr. phosphat of lime 
51 ! .91 1 carbonat of lime 
185.266 silica. 
Given out 971.482 
Taken in 356.057 
Surplus 654.125 
Consequently the quantity of fixed matter 
given out of the s\ stem in ten days exceeded 
the quantity taken in by 615.425 grains. 
The silica taken in amounted to 219.548 gr. 
That given out was only. - 185.266 gr. 
Remains 34.282 
Consequently there disappeared 34.28 2 
grains of silica. 
The phosphat of lime taken in was 1.36.509 gr. 
That given out was - 274.305 gr. 
137.796 
Consequently there must have been form- 
ed, by digestion in this fowl, no less than 
137.796 grains of phosphat of lime, besides 
511.911 grains of carbonat. Consequently 
lime (and perhaps also phosphorus) is not a 
simple substance, but a compound, and 
formed of ingredients which exist in oat-seed, 
water, or air, the only substances to which 
the fowl had access. Silica may enter into* 
its composition, as a part of the silica had 
disappeared; but if so, it must be combined 
