38 THE SECRETIONS: 



albumen and yelk of egg, fibrin, boiled albumen, muscular 

 flesh, casein, and the protein-compounds generally. Certain 

 substances are not at all digestible, as, for instance, woody fibre, 

 husks of fruit, horn, hair, &c. We always observe a relation 

 between the degree of the changes requisite for the assimilation 

 of different sorts of nutriment, and the complexity of the di- 

 gestive apparatus. Hence, in the carnivora, the intestinal canal 

 is much shorter and simpler than in the herbivora. 



In the ruminantia, the first two stomachs do not secrete an 

 acid, true gastric juice, such as occurs in the stomachs of men 

 and carnivora, but a thin yellow saline fluid containing enough 

 alkaline carbonates to produce a marked effervescence on the 

 addition of an acid. Their nutriment (grass, hay, &c.,) after being 

 chewed and mixed with saliva, is first received into these sto- 

 machs, where it is soaked in the alkaline fluid, which dissolves 

 and takes up vegetable albumen and glutin. The fluid gra- 

 dually passes onwards into the third stomach, while the 

 insoluble portion returns to the mouth for a second mastica- 

 tion. The fluid obtained by pressure from the contents of 

 the first stomach (the paunch) contains, according to Tiede- 

 mann and Gmelin, carbonic acid and sulphuretted hydro- 

 gen, albumen in combination with soda, carbonate of ammo- 

 nia, and certain animal matters, one of which is volatile and 

 assumes a red tint on the addition of muriatic acid. In addi- 

 tion to carbonic acid and sulphuretted hydrogen gases, the first 

 two stomachs occasionally develop (especially after the use of 

 fresh clover) an extraordinary quantity of carburetted hydrogen. 

 The third stomach secretes an acid fluid, and in the fourth sto- 

 mach the acidity is much more marked, the substances dissolved 

 by the alkali being first precipitated and then redissolved in 

 the excess of acid. Finally chyme is produced, said to be ana- 

 logous to that which is formed in the stomachs of men and 

 carnivora. 



In birds the food is first moistened in the crop with a faintly 

 acid fluid ; from thence it passes into the proventriculus, where it 

 meets with a peculiar and very acid fluid, and it finally reaches 

 the muscular stomach, which effects its thorough trituration. 



On leaving the stomach the food enters the small intestine, 

 where it becomes mixed with the pancreatic juice and the bile. 

 Here it commences to be absorbed by the intestinal villi ; more- 



