IN MEDICAL SCIENCE. 37 



words already borrowed from Virchow, "a sum of vital 

 unities." The strictum and laxum, the increased and 

 diminished action of the vessels, out of which medical 

 theories and methods of treatment have grown up, have 

 yielded to the doctrine of local cell-communities, be- 

 lono-ins 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 ex- 

 isting state of physiological knowledge. Some of them 

 involve the microscopic discoveries of which I havo 

 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 ftmction, 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 ex- 

 ceptional 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 ap- 

 peal 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 popu- 



