106 Mr Carpenter o)i Unity of Function 



mark, that in the simplest organisms, that both animal and vege- 

 table, a permeable membrane is all the apparatus necessary 

 for absorption ; and that vessels only become requisite where 

 the fluid has to be conducted to a distant part, either to serve 

 for the nutrition of the system, or to undergo a change in its 

 own constituents. We have remarked, also, that the digestive 

 apparatus of animals is to be regarded rather as an appendage 

 to the absorbing organs, rendered necessai-y by the nature of 

 their food and mode of obtaining it, than as forming an essen- 

 tial part of the system. 



We shall now endeavour to analyse the excretory system in 

 a similar manner; but here we meet with greater difficulty from 

 the increased complexity of the function. We cannot regard 

 the rejection of the excrementitious portion of the food as a 

 part of the function of excretion as performed by animals, any 

 more than the reception of the food by the mouth is a part of 

 the function of absorption. It would be better, therefore, to 

 limit the term excretion to the throwing off" matter which has 

 been already assimilated. This process, which is constantly 

 taking place in most of the tissues of plants and animals, bears 

 a strong relation, in point of activity, with the tendency of each 

 structure to spontaneous decomposition. Thus the bones of 

 animals and the heart-wood of plants will exist almost for an 

 indefinite period after the death of the individuals ; and in them 

 little change takes place during life. In the softer tissues, on 

 the other hand, whose decomposition is so rapid after vitality 

 is extinct, the processes of interstitial deposition and absorp- 

 tion are vigorously performed throughout the whole existence. 

 Hence it may perhaps be inferred, that the power which living 

 bodies possess of resisting the usual decomposing influences of 

 heat, moisture, oxygen, &c., is due not so much to anything 

 essentially different in the affinities which hold together these 

 elements during life and after death, but to the vital actions 

 by which every particle exhibiting the least tendency to disor- 

 ganization is immt^diately removed, and replaced by matter 

 newly assimilated. It is a curious fact that after animal life 

 is extinct, a certain degree of organic life frequently remains, 

 by which the excretory functions go on for a time ; thus car- 



