58 FEEDS AND FEEDING 



furnish is converted into heat in the work of masticating, digesting, and 

 utilizing it. With roughages like hay and straw the proportion is much 

 larger. However, in the case of animals exercising normally the larger 

 part of the body heat is produced in the muscular tissues, since all 

 muscular contraction is caused by the oxidation, or burning, of nutrients 

 in the muscles. Even when the muscles are not actively contracting, some 

 heat is being generated in them, for they are even then under a greater 

 or less degree of tension. 



When an animal is given no food, the heat needed to warm the body, 

 the net energy required to carry on the vital processes, and the protein 

 and mineral matter necessary for the repair of the active tissues must 

 all come from nutrients previously stored within the body. The small 

 supply of glycogen in the liver and muscles is probably first used as fuel, 

 but this is soon gone. (60) Fat is the animal's chief reserve fuel, stored 

 when food is abundant, against times of scarcity, and is therefore the 

 main source of both heat and energy during starvation. When the 

 supply of fat begins to fail, the muscles and other protein tissues are 

 broken down more rapidly to furnish heat and energy, and the animal 

 finally perishes thru the impairment of its organs and the lack of body 

 fuel to carry on the functions of life. Carnivora, or flesh-eating animals, 

 withstand hunger longer than herbivora. While dogs and cats have lived 

 until their weights were decreased 33 to 40 per ct., horses and ruminants 

 will die when their weight has been reduced 20 to 25 per ct. Men have 

 voluntarily fasted for over a month, and dogs have survived fasts of 

 from 90 to 117 days without permanent ill effects. The age of the 

 animal influences the time at which death occurs from starvation, young 

 animals losing weight more rapidly and dying after a smaller loss of 

 weight than old ones. 



89. Regulation of body temperature. In order to keep the temperature 

 constant under varying external conditions and with daily supplies of 

 food differing in amount and heat producing power, warm-blooded 

 animals must possess a highly efficient means of heat regulation. This 

 is under the control of the nervous system and is accomplished by 

 governing both the loss and the production of heat. 



The most important means of controlling the loss of heat is by vary- 

 ing the circulation of the blood near the surface of the body. When the 

 body temperature rises, more blood flows to the capillaries of the skin, 

 increasing the loss of heat by radiation and conduction. It is this 

 which causes the flushing of the skin commonly observed when one 

 becomes heated. This means of regulation may be compared to opening 

 the windows when a room becomes too hot. If this means of control is 

 not sufficient to keep the body temperature normal, sweat is produced, 

 the evaporation of which cools the surface of the body. If the animal 

 has no sweat glands, as in the case of the dog, or only a few, as in the 

 case of swine, it will begin to pant, thus increasing the evaporation of 

 water from the mouth and the vaporizing of water from the lungs. If 



