428 ORGANIC CHEMISTRY. 



body, as fuel to sustain tjhe animal heat. It is taken 

 up by the blood, and burned in the capillary vessels, 

 as before described. This happens in the case of the 

 bear and other hybernating animals. Lying dormant 

 during the winter season, their fat is consumed, and 

 they emerge lean from their dens in the spring. Where 

 food is deficient and there is no accumulation of fat to 

 supply its place, the muscle and other portions of the 

 body are consumed, and death by starvation is the con- 

 sequence. 



1063. REPAIR OF THE TISSUES. As fast 



How are the 



tissues repair- as the worn out matter of the muscles 

 and other organs is removed, its place is 

 supplied in the healthy body by new material from the 

 blood. Through it, also, the phosphates of the soil 

 and the vegetable world are transferred to the skeleton 

 of the animal, and in smaller proportion to other parts 

 of the frame. The blood is itself renewed by the 

 materials of the food. 



1064. VARIETIES OF FOOD. It is implied 



Mention two 



classes of in the foregoing, that the two classes of 

 f ood ' substances which enter into the compo- 



sition of the food of animals, subserve very diiferent 

 purposes in the animal economy. The first class, of 

 which starch and sugar are the principal, serve, by their 

 gradual combustion, to sustain the animal heat. They 

 are included, as above stated, under the general name 

 of respiratory food. The protein bodies, on the other 

 hand, all of which contain nitrogen, are appropriated 

 in the formation of blood and muscle ; they make up 

 the sanguineous or plastic food. In view of the fact 



