JuLy 21, 1899. ] 
Thus there are dissenting opinions 
amongst physiologists, but in this connec- 
tion it is to be remembered that it is prac- 
tically impossible to obtain normal intestinal 
juice. The method consists in cutting out 
a portion of the intestine and attaching this 
by both ends to a fistula made in the body 
wall. In this way admixture with gastric 
or pancreatic juice is prevented, but the 
conditions are highly abnormal! and nega- 
tive results with fluid obtained in such a 
way are of little weight. Moreover, phys- 
iologists usually make their experiments on 
mammals, whereas a study of the lower 
groups gives support to the view that in- 
testinal cells can secrete ferments having 
the same properties as those of the stomach 
and pancreas. Thus, the Cyprinoid fishes 
lack a stomach and extracts of their intes- 
tines can digest fibrin. The alimentary 
canal of the Cyclostomes is a straight tube, 
entirely wanting in diverticula. Itis, there- 
fore, probably safe to conclude that the 
view expressed by Landois is essentially 
correct, although it is not to be understood 
by this that the succus entericus has any- 
thing like so powerful an action as the 
enzymes from stomach or pancreas. Its 
properties are the same in kind as these, 
but much feebler in degree. 
The third class of foods consists of fats. 
These, unlike proteids and sugars, are ap- 
parently insoluble in the various digestive 
fluids. It seems, however, that steapsin is 
able to saponify fat. That this process ac- 
tually takes place has been proven by 
chemical analysis made on the contents of 
the intestine of animals fed on fat. For 
this reason, and for others to be given be- 
low, it is generally supposed that fat enters 
the intestinal epithelium as soap and glyc- 
erine. The evidence is, however, some- 
what contradictory, and this question can 
hardly be considered absolutely settled. 
The second phase of the digestive process, 
absorption, consists of the passage of the 
SCIENCE. vi 
prepared food through the epithelium of 
the intestine; in reality, its entrance into 
the body, for hitherto it has been outside. 
This food, as has been seen, is in solution, 
and the older physiologists considered its 
entrance to be either a mere soaking 
through or else an osmatic process. But it 
has been shown that this view is erroneous. 
Without discussing what the actual process 
may be in intravitam staining, it is known 
that living protoplasm behaves differently 
with different stains. Living spermatozoa 
can be stained differentially, while protozoa 
will take up certain anilines and wholly re- 
sist the action of others. Thatis, protoplasm 
has the power of resisting the entrance of 
certain substances. This power is clearly 
demonstrated by the epithelium of the in- 
testine. The laws of diffusibility do not 
hold true. For example, if a solution con- 
taining equal parts of sodium sulphate and 
glucose be allowed to act on the living in- 
testinal mucus membrane, the glucose will 
be almost entirely absorbed and the sodium 
sulphate scarcely at all. Yet the salt is 
much more diffusible than the carbohy- 
drate. The epithelial cells, then, possess a 
selective power which is obviously depend- 
ent upon the activity of their protoplasm. 
That this is of great importance to the or- 
ganism needs no emphasizing. 
The entrance of proteids and sugars has 
not been studied cytologically. Such an 
investigation, although of the utmost im- 
portance, presents extreme difficulties. The 
preliminary process essential to mounting 
would probably take out of the cells all 
such substances, and the work would neces- 
sarily have to be done on fresh cells. But 
proteid reactions are obscure and indefinite, 
and this, along with the technical difficul- 
ties in the way, a magnification of 750-1,000 
diameters being necessary, has evidently 
discouraged such researches, and our actual 
knowledge on this point is nil. Having 
entered, however, it has been satisfactorily 
