OF THE INTESTINAL VILLI. 11 



take place within the digestive tube, but exterior to the organism. 

 The second will include those which present themselves after the 

 alimentary matter is taken up into the animal body, and becomes 

 buried in its substance. The first group of processes are me- 

 chanical and chemical in their nature. They may be considered 

 in a great measure as peculiar to the animal, although even 

 vegetables throw out from their roots matter which, acting on 

 some of the materials of the surrounding soil, prepare these for 

 absorption. 



The second group of processes is common to animals and vege- 

 tables. In these, for the first time, are alimentary substances 

 taken into the tissues of the organism. In animals, as in plants, 

 as I have already pointed out, these alimentary substances are 

 drawn by a peculiar force into the interior of the cells, after 

 escaping from which they pass on by the absorbent system. 

 The chemist has not yet informed us of the change which the 

 matter has undergone during its passage from the cavity of the 

 gut, or from the soil, into the afferent lacteals and the sap- 

 vessels ; but if in vegetables, as in animals, this matter passes 

 into the cavities of the cells of the spongiole before it passes on 

 to the sap-vessels, then it is highly probable that the organizing 

 and vitalizing part of the function of digestion commences in the 

 cells of the spongiole and of the extremity of the villus. 



The extremity of the fibril of the root of a plant elongates by 

 the cells added to its tissue by the germinating spongiole. The 

 spongiole is, therefore, an active organ of growth as well as of 

 absorption. It is to the fibril of the root, what I have denomi- 

 nated in the animal tissues, the nutritive centre. I conceive it to 

 be probable, therefore, although as to this I have made no obser- 

 vations, that absorption by, and elongation of, the febril of the 

 root, vary inversely as one another. This supposition is founded 

 on the assumption, that the cells of the spongiole do not absorb 

 by transmission but by growth and solution. 



In the villi of the intestines of animals, my own observations 

 lead me to believe that absorption by growth and solution is the 

 process which actually takes place. 



The vesicular extremity, like the spongiole of the root fibril, 

 is the primitive nutritive centre of the villus. The villus 



