THE MAINTENANCE OF THE ANIMAL HEAT. 381 



to indicate that there are heat-accelerator-centers as well as 

 heat-inhibitory -centers. These have been localized especi- 

 ally in the region of the floor of the brain occupied by the 

 corpora striata. These centers in a reflex way stimulate 

 the centers of the spinal cord to greater heat production, or 

 inhibit them and so lessen the heat production. In this 

 way it is believed the heat equilibrium is so successfully 

 maintained. 



Under normal conditions these heat centers are adjusted 

 or set for a temperature of 37 l /io C., but in abnormal con- 

 ditions, such as fevers, they may become set or adjusted 

 for a higher temperature. Experiments on the lower 

 animals show that they may also be set for temperatures be- 

 neath the normal. It would be interesting to know just what 

 it is in the case of fevers which changes the readjustment 

 of these centers from the normal point to the fever point. 

 But this information is not at hand. Possibly some of the 

 poisons of the disease may act as an irritant upon these 

 centers and thus disturb the equilibrium. Unfortunately, 

 too, we have no knowledge yet in what specific manner 

 such drugs as quinine act in the reduction of these fever 

 temperatures. 



It is, of course, not necessary to say that these thermo- 

 genic nerves running to the various tissues in the body are 

 not anatomically distinguishable, but that the existence of 

 such centers and such nerves is based wholly upon physio- 

 logical grounds. 



QUANTITATIVE DETERMINATIONS OF THE SOURCE AND EXPEND- 

 ITURE OF HEAT. 



Heat may be measured just as corn or wheat. The unit 

 of heat measure is called the calorie. A calorie of heat is 

 the amount of heat necessary to raise the temperature of one 

 gram of water from zero degrees to one degree C. Or, de- 

 fining it more generally, a calorie is the amount of heat re- 

 quired to raise one gram of water one degree C. As the 

 amount of water in any given case can be accurately meas- 



