ABSORPTION AND ULCERATION. 403 



XXIII ABSOEPTION, ULCEEATION, AND THE 

 STKUCTUEES ENGAGED IN THESE PEOCESSES. 



EVERY organic cell, the most simple as well as the most 

 complicated, when a separate organism, or when a part of a 

 more highly organised being, existing as a mere magazine of 

 matter, or performing some of the more striking of the vital 

 functions, invariably exhibits a phenomenon which is ante- 

 cedent to all others absorption from without of materials 

 for its own growth. 



The various kinds of cells in any organism differ from one 

 another in this respect, that they have the power, each after 

 its kind, of selecting and procuring from the circulating 

 medium, or from other sources, the sort of matter necessary 

 for their own growth : or they have the power of elaborating, 

 or of conducing to the chemical change of the matter which 

 is absorbed by them. In this respect, the component cells of 

 animals and vegetables resemble the various species of beings 

 of which they form parts : they have not only the power of 

 selecting food, but the various species out of the same kind 

 of food are formed of matter and of parts which are specifically 

 different. 



A most important circumstance in the history of cellular 

 phenomena is the duration of existence of a cell. Like the 

 various species of animals and vegetables, each species of cell 

 has its own average term of existence, each after its kind. 

 This average term is nevertheless contingent on the amount 

 of action which each species may, by peculiar circumstances 



