DOMESTIC ANIMALS 



the animal. Thus in cattle the alimen- 

 tary tract is twenty times as long as the 

 body, in sheep and goats twenty-seven 

 times, in the hog seventeen times, in the 

 horse and ass eleven or twelve times, 

 and in the dog only four times. 

 The capacity of the alimentary tract is 

 800 pounds in cattle, 450 pounds in the 

 horse, 65 pounds in the hog, and 25 

 pounds in the dog. In cattle the feed 

 requires three or four days to pass 

 through the alimentary tract. About 

 the same length of time is occupied by 

 the digestive processes in the horse, 

 sheep and goat. In hogs, on the other 

 hand, the complete process does not ex- 

 tend beyond 36 hours and in dogs not 

 longer than 15 hours. The time re- 

 quired for digestion naturally varies ac- 

 cording to the character and condition 

 of the feed. Thus in cattle, green, suc- 

 culent forage may pass through the ali- 

 mentary tract in two days. On the other 

 hand, dry hay may occupy 14 days or 

 more in the same process. In feeding 

 experiments in which the ration is 

 changed during the course of the experi- 

 ment for purposes of comparison, it is 

 customary to allow six to eight days for 

 the last remains of the previous ration 

 to appear in the manure. 



The digested and dissolved portion of 

 the feed together with the water is ab- 

 sorbed through the walls of the stomach 

 and intestines, chiefly the latter, and 

 carried by means of the blood and lymph 

 vessels to the tissues. A curious trans- 

 formation takes place in the protein of 

 the feed. After the protein has been 

 changed into albuminoses, peptones and 

 crystalline bodies, it is retransformed 

 in the walls of the stomach and intes- 

 tines into ordinary protein and appears 

 as such in the blood vessels. An enzym 

 in the wall of the stomach, probably 

 identical with rennet, has the power of 

 reuniting the peptones and albuminoses 

 into the original proteids. The restored 

 protein although chemically like the 

 original is physically very different. It 

 is animal protein whereas that in the 

 food is vegetable protein. The animal 

 is thus capable of partly disintegrating 

 and immediately reconstructing the food 

 protein according to the organic require- 

 ments of the particular animal. 



The fats—Likewise the fats although 

 at first split up, as above described, into 

 free fatty acids and glycerin, and later 

 saponified in part, are largely recon- 

 structed from their digestive products 

 in the walls of the stomach and intes- 



tines and appear in the chyle as a neu- 

 tral, animal fat. Some of the food fat, 

 however, may pass through the walls of 

 the alimentary tract into the chyle with- 

 out change. 



The carbohydrates after digestion are 

 absorbed chiefly by the blood vessels and 

 only to a very slight extent in the chyle. 

 When absorbed they are in the form of 

 grape sugar, galactose or lactic, butyric 

 and acetic acids and their salts. The 

 pentosans in the feed apparently go 

 through the same processes as the carbo- 

 hydrates. 



Water and mineral salts are absorbed 

 into the blood chiefly through the walls 

 of the intestines and to a much less ex- 

 tent through the stomach. The absorp- 

 tion of digested food products follows the 

 ordinary laws of capillarity, filtration 

 and diffusion. The absorbent surface in 

 horses and cattle is five times as great 

 as in the hog. 



The undigested portion f the feed 

 passes on into the large intestines where 

 finally the process of digestion is super- 

 seded by that of decomposition due to 

 bacteria. The material which is ulti- 

 mately discharged as feces or manure 

 consists of actually indigestible mate- 

 rial, more or less digestible material 

 which has failed to be digested, some 

 of the digestive juices and bile, 

 epithelial cells from the intestinal walls, 

 and waste products from the tissues of 

 the body. The manure contains, there- 

 fore, considerable nitrogenous substance 

 as well as mineral matter. In birds 

 the feces contain also the urinary ex- 

 cretion. 



Function and character of blood 



As already indicated the blood car- 

 ries all of the absorbed food materials 

 throughout the body and delivers them 

 to the tissues where they are needed. It 

 also carries back the waste materials 

 due to disintegration of tissue and dis- 

 charges them into the intestines, kid- 

 neys, lungs, or sweat glands of the skin. 

 The blood also carries oxygen from the 

 lungs to various parts of the body where 

 it is used in the process of metabolism. 

 The blood consists of a fluid or serum 

 containing red and white corpuscles. 

 The red color of the blood is due to 

 hemoglobin in the red corpuscles. 

 Hemoglobin is scarlet when charged 

 with oxygen but becomes brownish red 

 when the oxygen is replaced by carbon 

 dioxid in the tissues. In cases of 

 anemia the number of red corpuscles is 

 below the normal and the blood is there- 



