334 SCIENCE PROGRESS. 



is recognising that, until the factors of that bald, but as 

 yet necessary, expression "Vital Action" can be analysed 

 and harmonised with physical forces, little progress can be 

 made towards an intimate knowledge of the essence of 

 life. 



The history of the development of our ideas concerning 

 the absorption of nutriment is an interesting one, as indi- 

 cating how ignorant we as yet are of much that is concerned 

 in a process which until recently was thought to be ex- 

 plicable upon purely " physical " grounds. 



The classical work of Dutrochet, published at the close of 

 the third decade of the century, was hailed soon after by 

 physiologists as giving an indication of the lines upon 

 which the movements of fluids through membranes in the 

 living animal could be explained. It appeared to be beyond 

 doubt that osmotic action would alone suffice to account for 

 the phenomena of absorption so far as they had then been 

 studied. 



Yet, as will be evident from the sequel, we have now to 

 admit that, though osmotic action is a factor, and often of 

 great importance, experiment shows that another factor has 

 to be considered, viz., the living condition of the cells of the 

 membrane through which the solutions pass. 



A glance at our present knowledge of the main ana- 

 tomical points in the structure of the intestinal membrane 

 must precede our physiological considerations. 



A multitude of villous processes are clad with specialised 

 columnar cells, whose inner blunt ends rest upon the paren- 

 chyma of the organ somewhat condensed at its periphery. 

 A network of blood capillaries is in many places in im- 

 mediate contact with the ends of these cells, and in the 

 depths of the parenchyma (a more marked structure in 

 carnivors than in herbivors) is imbedded a lacteal tube with 

 blind end and distinct endothelial wall. The epithelial cells 

 are but loosely attached at their inner ends, though cemented 

 together at their sides, and their renewal according to 

 Bizzozero, Heidenhain, Cloetta, and Schaffer is effected 

 from below, from the cells of the crypts of Lieber- 

 kuhn, which divide in a plane at right angles to the long axis 



