and methods of treatment have grown up, have yielded to the doctrine
of local cell-communities, belonging to this or that vascular district,
from which they help themselves, as contractors are wont to do from the
national treasury.

I cannot promise to do more than to select a few of the points of
contact between our ignorance and our knowledge which present particular
interest in the existing state of our physiological acquisitions.
Some of them involve the microscopic discoveries of which I have
been speaking, some belong to the domain of chemistry, and some have
relations with other departments of physical science.

If we should begin with the digestive function, we should find that the
long-agitated question of the nature of the acid of the gastric juice is
becoming settled in favor of the lactic. But the whole solvent agency of
the digestive fluid enters into the category of that exceptional mode of
action already familiar to us in chemistry as catalysis. It is therefore
doubly difficult of explanation; first, as being, like all reactions,
a fact not to be accounted for except by the imaginative appeal to
"affinity," and secondly, as being one of those peculiar reactions
provoked by an element which stands outside and looks on without
compromising itself.

The doctrine of Mulder, so widely diffused in popular and scientific
belief, of the existence of a common base of all albuminous substances,
the so-called protein, has not stood the test of rigorous analysis. The
division of food into azotized and non-azotized is no doubt important,
but the attempt to show that the first only is plastic or nutritive,
while the second is simply calorifacient, or heat-producing, fails
entirely in the face of the facts revealed by the study of man in
different climates, and of numerous experiments in the feeding
of animals. I must return to this subject in connection with the
respiratory function.

The sugar-making faculty of the liver is another "catalytic" mystery, as
great as the rest of them, and no greater. Liver-tissue brings sugar out
of the blood, or out of its own substance;--why?

Quia est in eo
Virtus saccharitiva.

Just what becomes of the sugar beyond the fact of its disappearance
before it can get into the general circulation and sweeten our tempers,
it is hard to say.

The pancreatic fluid makes an emulsion of the fat contained in our food,
but just how the fatty particles get into the villi we must