Villi in Man and certain of the Mammalia, 173 



first group of processes are mechanical and chemical in their 

 nature. They may be considered in a great measure as pe- 

 culiar 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 

 vegetables. In these, for the first time, are alimentary sub- 

 stances 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 

 cells, after escaping from which they are taken up by the ab- 

 sorbent 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, 

 tjiis matter passes through the coats and is lodged in the ca- 

 vities 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 

 liy 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 

 denominated in the animal tissues the germinal spot. I conceive 

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

 observations, that absorption by, and elongation of, the fibril 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 observa- 

 tions lead me to believe that absorption by growth and solu- 

 tion is the process which actually takes place. 



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

 is the primitive germinal spot of the villus. The villus origi- 

 nates in a cell, one of those which form the last deposit from 

 the substance of the yelk. During the development of the 

 villus, this spot or cell was employed only in procuring mate- 

 ^•ials for the growth of the organ. In the perfect animal 

 the formative ftmction of the spot ceases ; its action becomes 



