1098 ANIMAL HEAT 



may justly be concluded that muscular rest must lessen its production, 

 although it can never stop it altogether. For similar reasons it may 

 be assumed that paralyzed muscle must liberate only a very slight 

 amount of heat, a fact which fully accounts for the coldness of these 

 parts as well as for the feeling of chilliness experienced by the para- 

 lytic person. It is true, however, that in these cases* the circulatory 

 system is by no means performing its function properly so that the 

 factor just mentioned is usually augmented by a greater loss of heat. 

 An experiment directly bearing upon this question, is the following: 

 If a rabbit is curarized and is kept alive by artificial respiration, any 

 alteration in the temperature of the atmosphere changes its body- 

 temperature very markedly in the same direction. Since this agent 

 paralyzes the motor plates of the muscles, it nullifies the action of the 

 most efficient heat-producing organ of the body and permits the entire 

 system to become more fully dominated by outside influences. 



The beneficial effect of muscular activity is also betrayed by the 

 phenomenon of shivering, an involuntary reaction following an undue 

 drop in the body-temperature. The object of this quivering is to 

 produce heat to counterbalance the loss. If this is not sufficient, 

 this reflex reaction is augmented by voluntary muscular contractions 

 and mechanical impacts, the purpose of which is to augment the circu- 

 lation. The efficiency of this reflex mechanism is also betrayed by 

 the changes resulting in the metabolism of the warm-blooded animals 

 in consequence of variations in the temperature of the atmosphere. 

 Thus, it is a well-known fact that low temperatures increase and high 

 temperatures decrease the metabolism and hence, also the production 

 of heat. During the cold seasons of the year we are much more active. 

 We eat more and gain in weight perceptibly, because a certain pro- 

 portion of the excess material is stored. In hot weather, on the other 

 hand, we are slack and incline to rest and sleep to lessen the production 

 of heat. 



Cold and warm baths possess a similar influence, the immersion 

 of the body in water of 32 to 34 C. for a minute or two sufficing to 

 increase the output of carbon dioxid considerably. This change, 

 however, appears only if the person is in tonus and does not counter- 

 act this reflex reaction by remaining passive and willfully relaxing 

 his muscles. In the latter case, the carbon dioxid output would be 

 decreased, causing the body-temperature to drop. Furthermore, this 

 drop need not always become apparent immediately; in fact, since 

 the cooled external parts must slowly replenish the heat which they 

 have lost at the expense of the internal structures, from 15 to 20 min- 

 utes may elapse before it is experienced. As soon, however, as the 

 subcutaneous parts have regained their heat, the rectal temperature 

 returns rapidly to normal. This process of equalization may be 

 greatly hastened by voluntary muscular contractions as well as by 

 deep and superficial massage. Another means of varying the pro- 

 duction of heat lies in the character of the food ingested. Thus, the 



