THE SCALE OF ASSIMILATIONS. 145 



the cud, is a permanent building, in order that eating may consume 

 the bulk of their waking hours. 



So much for the muscular coat of this series, whose activity con- 

 stantly builds the plastic walls into new and ever-varying chambers, 

 in which the functions of the place are carried on ; for every pass- 

 ing wrinkle on the surface is a fresh thought and artifice of diges- 

 tion and assimilation. 



But as we are not on a medical quest, let us henceforth rather 

 pursue the food that is assimilated, and the organs which take, and 

 convey it, than the portion which is rejected, or the extensive 

 system of public works that underlies the thoroughfares of the 

 human city. Respecting this department it will be sufficient to 

 note the principle, that series governs here as elsewhere ; that what 

 is renounced as useless by the first cavity becomes the especial food 

 of the second; that the leavings of the second are the table of the 

 third ; and finally that what is of no use to the animal kingdom 

 becomes the support of the vegetable world. Thus the purposes 

 of the aliment are drawn forth one by one in regular order, and 

 with a thrift that can go no further, the last use returns to the first, 

 in the fertility of the earth, in the precious yield of the plant, and 

 in the support of the animal, which reverts to the human body by 

 this circle of renunciation and absorption. 



Let us now note the distinct divisions or joints of the alimentary 

 tube, which prove that a series of different digestions and assimila- 

 tions are performed therein. Observe the mouth, which is guarded 

 by the lips, and then by the teeth, against any unmeet intrusion of 

 the food. This is the type of what takes place five times over in 

 the lower parts of the series. Thus the entrance to the pharynx 

 and gullet is analogously guarded. The entrance to the stomach is 

 secured by strong muscular lips, which are only opened by the mus- 

 cular wave flowing down the oesophagus, and playing upon the wedge 

 of food. The exit from the stomach is a similar lip or ring, which 

 is likewise opened by the successive action of the stomach and the 

 aliment. And so forth. The cause therefore which determines 

 the passage of the food from cavity to cavity, is that the first cavity 

 has assimilated its portion, and digested its portion, and having no 

 longer any affinity for the latter, the walls contract against it, and 



