THE INFLUENCE OF INTERNAL FACTORS 63 



The numerous experiments made on man by Speck [1883], Loewy 

 [1890], and Johansson [1897, 1898, 1904] show that in man at least 

 no chemical regulation of heat production exists apart from distinct 

 muscular activity. At low surrounding temperatures the respiratory 

 exchange is never increased unless the subject is unable to suppress 

 shivering or other movements. 



Krarup [1902], experimenting on rabbits, found that in these 

 animals the increase in metabolism observed when the surrounding 

 temperature was lowered was in almost all cases accompanied by visible 

 muscular movements, though he records two exceptions. After ure- 

 thane the movements were generally absent and the respiratory ex- 

 change rose and fell directly with the temperature, but when they 

 were present the variations were in the opposite direction, as in normal 

 animals. After pithing, all movements ceased and the metabolism 

 varied directly with the temperature. The same is the case also after 

 curari as found by Velten [1880]. Velten's results show that if a 

 chemical heat regulation can be induced from the central nervous 

 system the stimulus must travel along the motor nerves, since these 

 alone are affected by curari. This does not appear likely, and the 

 most probable conclusion seems to be that just as no nervously in- 

 duced increase in functional activity is possible without a corresponding 

 increase in metabolism so also there is no nervously induced increase 

 in metabolism without an increase in functional activity. 



The Thyroid Gland. 



Certain glands possessing internal secretion have been shown to 

 influence the standard metabolism in man and mammals, and this is 

 the case especially with regard to the thyroid gland. 



Magnus-Levy [1897] found in a long series of experiments on a 

 patient with myxcedema that the standard metabolism was remarkably 

 low (2 -9 c.c. oxygen per kilogram and minute) though not lower than it 

 has been found occasionally in perfectly normal men. When the patient 

 was treated with thyroid tablets it rose during three weeks to 5*5 c.c. 

 per kilogram and minute. It then fell off again towards the former 

 figure, being 3 -3 after 7 weeks and 3-0 later (7 to 13 weeks). The treat- 

 ment was repeated twice with the same result. In the intervals between 

 the treatments the myxcedematous symptoms were almost absent at 

 first but they began to appear each time before the treatment was 

 renewed. 



In 'normal people treatment with thyroid preparations sometimes, 



