318 DR ALISON'S OBSERVATIONS ON 



themselves, of adding to any of the animal textures except the fat ; but that they 

 are the chief material on which the oxygen of the air acts to keep up the animal 

 heat. 2d, That the main reliance of the animal body for the nom-ishment of all its 

 parts must be on the former class of aliments ; their adequacy for that purpose 

 being beautifully exemplified in the life of the chick in ovo, where all the textures 

 are formed out of the albumen, partially converted into gelatin in the process, and 

 with the addition of a small quantity of oil from the yolk ; the oxygen of the air 

 being essential to the vital movement, but no farther concerned in the results, 

 than as it carries off a certain portion of the carbon and hydrogen from the mov- 

 ing matter, and so occasions a loss of substance during the process of incubation. 

 3d, That the azotised ingesta, or the textxu-es formed from them, are themselves 

 liable to this action of the ox3^gen when the non-azotised ingesta are deficient ; 

 and, therefore, that an important use of the non-azotised food is, to protect the 

 albuminous constituents of the blood and the animal textures, from an influence 

 of the oxygen of the air, which, but for that protection, would be injurious, and 

 ultimately destructive. And I may perhaps be allowed to state what seem to me 

 the most important results, both as to Physiology and Pathology, which are in- 

 volved in these principles. 



1. Our ideas of the use of the digestive apparatus of animals are rendered 

 much more simple and precise. I have stated, indeed, that Dumas appears to 

 have erred in the way of extreme simplification, when he says that " an animal 

 only assimilates" {i. e. selects and attracts) " organic structures already formed ; 

 that he forms none ;" that " digestion is therefore a simple process of absorption, 

 soluble substances passing directly into the blood [i.e. by the veins), for the 

 most part without alteration, and insoluble substances making their way into the 

 chyle after having been sufiBciently comminuted, to be imbibed by the lacteals." 

 But although we suppose that certain transformations, as well as simple absorp- 

 tion, must be commenced, at least, in the digestive organs, we are sure that no 

 complication of apparatus is necessary for accomplishing them ; the most impoi"t- 

 ant of all transformations necessary to life taking place in vegetables, and in or- 

 gans of extreme simplicity. 



The following may be stated as the purposes which are served by the diges- 

 tive apparatus of every kind of animal, whether carnivorous or herbivorous, and 

 the greater complexity of the arrangements in the latter tribes must be considered 

 as intended merely to present a larger surface, and afford a longer time, for the 

 accomplishment of changes which are, in fact, identical in kind, and all of whicli 

 may be effected in the simplest form of apparatus. 



(1.) This apparatus is obviously necessary, as stated by Cuviee, for the sup- 

 port of textures whose vital action is dependent on a continuous supply of nou- 

 rishment, to afford that continuous supply from aliments, the reception of which, 

 in the case of animals, is only occasional, and sometimes long delayed. 



(2.) It is useful, as providing for the separation and immediate expulsion 



