

REGULATION OF THE TEMPERATURE. 329 



cutaneous nerves (by thermal stimulation), or the nerves of the intestine and the 

 digestive glands (by mechanical or chemical stimulation during digestion or inani- 

 tion), may be irritated, whereby impressions are conveyed to the heat-centre, which 

 sends out impulses through efferent fibres to the depots of potential energy, either 

 to increase or diminish the extent of the transformations occurring in them. The 

 nerve channels herein concerned are entirely unknown. Many considerations, 

 however, go to support such an hypothesis ( 377). 



[Thermotaxic Mechanism, Thermal Nerves and Centres. Just as the respiration and the 

 state of the blood-vessels are regulated from a central focus, so the question arises, does the 

 same obtain with regard to temperature. Studying this question, however, it must be borne 

 in mind that thermometric observations alone are not sufficient ; the true test must be calori- 

 metric. Sir Benjamin Brodie observed that in a case of injury of the spinal cord in the neck 

 the temperature in the thigh rose very high. In some cases the temperature falls. "Wood has 

 shown that section of cord above the origin of the splanchnics leads to decided increase in the 

 amount of heat dissipated, but to a decided diminution of heat-production. The vaso-motor 

 paralysis has much to do in these cases with the loss of heat. In warm-blooded animals, 

 exposed to a high temperature, the heat-production is diminished, but when they are exposed 

 to a low temperature it is increased. If a warm-blooded animal's medulla oblongata be divided, 

 there is a fall of temperature, chiefly due to its vaso-motor paralysis, and such an animal behaves, 

 as regards the effect of heat and cold, exactly like a poikilothermal animal, i.e., its metabolism 

 and heat-production are increased by cold and diminished by heat. If, however, the incision 

 be made above the pons, so as to leave the vaso-motor centre intact in the dog, there is a rise of 

 the temperature and increased heat-production for 24 hours afterwards. This suggests the idea 

 that this region is traversed by inhibitory nerves, so that when they are cut off from their centres 

 situate above, the augmentor nerves can act more vigorously. This suggests the existence of 

 thermo-inhibitory centres situate higher up in the brain. If an animal be curarised, not only 

 is there paralysis of voluntary motor acts, but on stimulating an ordinary motor nerve, not 

 only is there no muscular contraction, but there is no rise of temperature of the muscles supplied 

 by that nerve. In such an animal the temperature rises and falls with the temperature of the 

 surrounding medium. Even although the respirations be kept constant and the vaso-motor 

 nerves intact, the thermogenic activity of muscles, therefore, seems to be dependent on their 

 innervation.] 



[Cerebral Centres. Apart from the cortical heat centres ( 377), Ott, Aronsohn, Sachs, 

 Richet and others have shown that if a needle be thrust through the skull and brain, so as 

 to injure certain deeper-seated parts, there is a rise of temperature and increased heat-produc- 

 tion for several hours. The experiment may be repeated several times in the same rabbit. Ott 

 gives three areas which, when so injured, cause these effects (1) a part of the brain in the 

 median side of the corpus striatum, and near the nodus cursorius ; (2) a part between the corpus 

 striatum and the optic thalamus ; and (3) the anterior end of the optic thalamus itself. From 

 the effect of atropin, Ott suggests the existence of spinal centres as well.] 



The following phenomena indicate the existence of mechanisms regulating the 

 production of heat : 



(1) The temporary application of moderate cold raises the bodily temperature, 

 while heat, similarly applied to the external surface, lowers it ( 222 and 224). 



(2) Cooling of the surroundings increases the amount of C0 2 excreted, by in- 

 creasing the production of heat, while the O consumed is also increased simul- 

 taneously; heating the surrounding medium diminishes the C0 2 ( 127, 5). 



D. Finkler found, from experiments upon guinea-pigs, that the production of heat was more 

 than doubled when the surrounding temperature was diminished 24 C. The metabolism of the 

 guinea-pig is increased in winter 23 per cent, as compared with summer, so that the same rela- 

 tion obtains as in the case of a diminution of the surrounding temperature of short duration. 



C. Ludwig and Sanders- Ezn found that in a rabbit there was a rapid increase in the amount 

 of C0 2 given off, when the surroundings were cooled from 38 to 6 or 7 C. ; while the excre- 

 tion was diminished when the surrounding temperature was raised from 4-9 to 35-37, so 

 that the thermal stimulation, due to the temperature of the surrounding medium, acted upon 

 the combustion within the body. Pfliiger found that a rabbit which was dipped in cold water 

 used more and excreted more C0 2 . 



If the cooling action was so great as to reduce the bodily temperature to 30, the exchange of 

 gases diminished, and where the temperature fell to 20, the exchange of gases was diminished 

 one-half. It is to be remembered, however, that the excretion of C0 2 does not go hand in 

 hand with the formation of C0 2 . If mammals be placed in a warm bath, which is 2 to 3 

 higher than their own temperature, the excretion of C0 2 and the consumption of are increased, 



