Blood and Blood Vessels. 223 



drawn between digestion and absorption. They are parts 

 of one great series of processes. Not only so, but the term 

 absorption is misleading, as it suggests purely physical 

 processes, which latter must always be dealt with very 

 cautiously by physiologists. 



If, for example, we regard the capillaries of the alimen- 

 tary tract as glands, it will no longer be impossible to 

 understand that the peptones of digestion are not repre- 

 sented by peptones in the blood, the great stumbling-block 

 of physiologists for long enough. 



Intracellular digestion is not confined to invertebrates. 

 The cells of the digestive tract, those of the capillaries 

 included, have not wholly forgotten the amoeboid habits of 

 their embryonic ancestors. They are specialized, it is true, 

 but not wholly altered. To suppose that digestion, or the 

 physical and chemical alteration of food ends within the 

 cavity of the alimentary tract, is to overlook a large part of 

 the truth. Food is changed there by virtue of the digestive 

 secretions, but all is not thus done. In fact, what is com- 

 monly termed digestion is only the beginning of a long 

 series of processes which go on in the cells of the structures 

 of the tract, the capillaries included, in the blood itself to 

 some extent, and which continue under the name of meta- 

 bolism in the tissues themselves. But it is the separation 

 and isolation in the mental conception of the student, of 

 what must be linked in one long chain, that is to be especi- 

 ally dreaded in the modern teaching of physiology. 



A student may throw a great part of the facts of his 

 physiology overboard after his examination, but the influ- 

 ence of his teaching must last for good or evil in all his 

 thinkings as a practitioner. That a sounder view of the 

 processes of digestion, etc., would greatly modify practice, 

 and especially would explain present failures and successes, 

 is clear to myself. Any attempt, however, to make this 

 evident to others must be left for another occasion. 



It may, without exaggeration, be said that the applica- 

 tion of the principles of evolution to morphology has revo- 

 lutionized the teaching of that subject. But, strangely 



