VARIATIONS IN THE HEAT OF THE BODY. 451 



in the muscular tissue has been observed in experiments with portions of 

 muscle from the frog. Not only was there an absorption of oxygen and 

 exhalation of carbon dioxide after the muscle had been removed from the 

 body of the animal, but an elevation in temperature of about one degree 

 Fahr. (0*55 C.) was noted following contractions artificially excited (Mat- 

 teucci). Observations upon the influence of mental exertion on the tempera- 

 ture of the body have not been so many, but they are, apparently, no less 

 exact in their results. Davy observed a slight but constant elevation during 

 " excited and sustained attention." Lombard noted an elevation of tempera- 

 ture in the head during mental exertion of various kinds, but it was slight, 

 the highest rise not exceeding O05 Fahr. (O027 C.). According to Bur- 

 dach, the temperature of the body is increased by the emotions of hope, joy, 

 anger and all exciting passions, while it is diminished by fear, fright and 

 mental distress. 



It is evident that if animal heat be one of the necessary, attendant phe- 

 nomena of nutrition, it must be greatly influenced by conditions of the circu- 

 lation. It has been a question, indeed, whether the modifications in tem- 

 perature, produced by operating upon the vaso-motor nerves, be not due 

 entirely to changes in the supply of blood. It is certain that whatever deter- 

 mines an increased supply of blood to any part raises the temperature ; and 

 whenever the quantity of blood in any organ or part is considerably dimin- 

 ished, the temperature is reduced. This fact is constantly illustrated in 

 operations for the deligation of large arteries. It is well known that after 

 tying a large vessel, the utmost care is necessary to keep up the temperature 

 of the part to which its branches are distributed, until the anastomosing ves- 

 sels become enlarged sufficiently to supply the quantity of blood necessary 

 for healthy nutrition. 



Influence of the Nervous System upon the Production of Animal Heat 

 (Heat-Centres}. The local influences of the vaso-motor nerves upon calori- 

 fication operate mainly if not entirely through changes in the nutrition of 

 parts, produced by variations in blood-supply. These influences will be fully 

 considered in connection with the physiology of the nervous system. 



The general temperature of the body may be modified through the nerv- 

 ous system by reflex action, and this implies the existence of nerve-centres, or 

 of a nerve-centre, capable of influencing the general process of calorification. 

 Experiments have been made, chiefly on parts of the encephalon, with the 

 view of determining the existence and location of heat-centres. In a recent 

 publication by Ott (1887), four heat-centres are recognized, irritation of 

 which by puncture increases the temperature of the body in rabbits by several 

 degrees (4 to 6 Fahr., or 2-2 to 3-3 C.). These four centres are as fol- 

 lows: 1, in front of and beneath the corpus striatum (Ott); 2, the median 

 portion of the corpora striata and the subjacent parts (Aronsohn and Sachs) ; 

 3, between the corpus striatum and the optic thalamus (Ott) ; 4, the anterior 

 inner end of the optic thalamus (Ott). Puncture of these parts is followed 

 by rise in temperature, which continues for a variable time, two to four days. 

 A similar centre has been described as existing in the dog, in the cortex of 



