VARIATIONS IN THE MEAN BODILY TEMPERATURE. 395 



nels necessary for the maintenance of this hypothesis. Nevertheless, 

 numerous phenomena indicate that such a view is not unjustifiable. 



Investigation has as yet furnished no adequate evidence as to the existence 

 of a heat-center. Tschetschechin and Naunyn, as well as Ott and Wood recently, 

 assume the existence in the brain (according to Ott in the anterior portion of the 

 optic thalamus) of a center that is supposed to exert an inhibitory effect upon 

 the combustion-processes in the body through fibers that descend through the 

 pons, medulla and cord; and accordingly destruction of this center or its con- 

 ducting paths would cause increased heat-production. Aronsohn and Sachs ob- 

 served transitory rise of temperature, with increased metabolism, after deep 

 puncture of the rabbit's brain several millimeters to one side of and behind the 

 anterior fontanel. Injuries of the caudate nucleus, optic thalamus, corpus cal- 

 losum, septum lucidum and trigone also cause similar phenomena. Confirmatory 

 evidence is given by Richet, who attributes this elevation of temperature to in- 

 creased heat-production. The animals eat more, yet lose flesh. Repeated cerebral 

 puncture eventually induces marasmus, reduction in temperature, as low as 26, 

 and death. Centers with an opposite function, namely, stimulating heat-produc- 

 tion, are said to be situated in the caudate nucleus, in the gray substance of the 

 septum lucidum and in the gray matter in front of and below the caudate 

 nucleus and in the tuber cinereum. After high division of the spinal cord heat- 

 regulation, heat-production and heat-dissipation are disturbed. 



The regulatory mechanisms governing heat-production can be recog- 

 nized from the following phenomena : 



1. As a result of the moderate, transitory influence of cold the bodily 

 temperature rises, while as a result of the like influence of heat upon the 

 external integument the temperature declines. 



2. Heat-production is increased by reduction of the surrounding 

 temperature, while the excretion of carbon dioxid and the consump- 

 tion of oxygen are at the same time increased. Heat-production is 

 diminished by increase of the surrounding temperature. The produc- 

 tion of carbon dioxid takes place principally in the muscles, without 

 contraction necessarily taking place at the same time. 



Human beings generate at o C. about twice as much heat as at a surrounding 

 temperature of 30 C. D. Finkler found in experiments on guinea-pigs that the 

 production of heat is more than doubled in vigorous animals in consequence of 

 a reduction in the surrounding temperature of about 24 C. Thus, during the 

 winter the metabolism of the guinea-pig was increased about 23 per cent, as com- 

 pared with the summer. It thus caused an alteration in heat-production in 

 general that is entirely analogous to that resulting from lowering of surround- 

 ing temperature of shorter duration. 



C. Ludwig and Sanders-Ezn have observed in rabbits, when the surrounding 

 temperature was reduced from 38 C. to 6 or 7, a rapid increase in the elimination 

 of carbon dioxid. Conversely, this was diminished in animals as the surrounding 

 temperature was raised from between 4 and 9 to from 35 to 37. The thermic 

 stimulation of the surrounding temperature must thus have had an effect also 

 upon the combustion-processes. In accordance with this fact is the observation 

 of Pfliiger, who found increased consumption of oxygen and increased elimination 

 of carbon dioxid in rabbits that had been immersed in cold water. When the 

 influence of the cold was so profound that the bodily temperature fell as low as 

 30, the gaseous interchange also diminished, and if the exposure continued until 

 the temperature fell to 20 the interchange became only half of the normal, 

 mammals are placed in a warm bath whose temperature exceeds that of the body 

 by 2 or 3 the elimination of carbon dioxid and the consumption of oxygen 

 increase in consequence of a stimulation of the metabolic processes. The elimina- 

 tion of urea also increases from the same cause. 



3. The application of cold to the external integument causes in part 

 involuntary muscular movement (shivering), in part voluntary muscular 

 movement. As a result of both heat is produced. 



