116 



METABOLISM AND NUTRITION 



The alterations of metabolism in the service of heat regulation do not 

 make their appearance, if the influence of the central nervous system on the 

 muscles be terminated either by curare poisoning or by section of the spinal 

 cord at a high level. This is shown by the following experiment of Velton 

 on a curarized rabbit. 



These facts naturally suggest that under normal circumstances the rise 

 in metabolism here being considered is due to muscular activity called out 

 by the central nervous system, and this is very generally assumed to be the 

 case. But a question arises as to whether gross, plainly visible muscular 

 movements necessarily occur. 



In small animals, such as mice, the bodily movements become very active 

 when the external temperature is greatly lowered. In dogs, on the other hand, 

 Rubner never observed any movements which were directly occasioned by the 

 heat or cold, although he emphasizes the statement that at the upper and lower 

 extremes of temperature marked unrest was at times to be observed. 



In the present writer's opinion, it is very difficult or probably impossible to 

 solve the question of the part taken by the muscles in the heat regulation by 

 experiments on animals, for there must always be a certain amount of muscular 

 tension and the like which can scarcely be estimated with any accuracy, although 

 the metabolism may be very considerably increased by them. Thus in experi- 

 ments by Johansson, the CO 2 -elimination in an ordinary resting condition, lying 

 in bed, was twenty to thirty-one per cent more than when great care was taken 

 to observe absolute muscular rest. Hence in order to exclude muscular move- 

 ments altogether, it is obviously necessary to carry out the experiments on per- 

 sons who are willing and able to enforce the desired state of relaxation of their 

 own bodies. 



From the experiments of Loewy it appears that within a period of one and 

 one-quarter to one and one-half hours the respiratory exchange does not al- 

 ways increase, even though the temperature fall considerably. But whenever 

 an increase did occur, if the experiment was being performed on an intelligent 

 individual intrusted with the regulation of his own respiration, shivering or 

 increased tone of the muscles was distinctly evident. By maintaining com- 

 plete rest for one and one-half hours Johansson was unable to secure any 

 evident influence of external temperature upon the excretion of carbon diox- 

 ide, although the body was naked and the temperature varied from 14 to 

 22 C. Under Rubner's direction, experiments continued from four to six 

 hours gave, on the whole, similar results. 



One is likely to conclude from these experimental facts that when mus- 

 cular movements are voluntarily suppressed, the production of heat in man 



