METABOLISM 21 



in the body are but little affected by them. It used to 

 be believed that metabolism was most active in early 

 spring, and that at this period every function was at its 

 highest degree of efficiency, a decline taking place as 

 summer advanced, with a gradual rise again in the 

 autumn. Later observations have shown, however, 

 that the demand for food, and presumably, therefore, 

 the activity of metabolism, is not less in summer than 

 in winter. The daily variations in metabolism, also, 

 would appear to be very slight if the influence of mus- 

 cular exertion and the taking of food be eliminated, but 

 there remains a certain amount of evidence to show that 

 metabolism is more active in the later part of the day 

 than in the earlier, the maximum being reached about 

 5 p.m., and the minimum about five o'clock in the 

 morning.* Medical experience would certainly seem to 

 show that ' vitality ' is less in the early hours of the 

 morning than at other times, and the need for stimulants 

 in asthenic conditions is then greater. 



The influence of * weather ' upon metabolism is a 

 subject of great interest to the practical physician, but, 

 unfortunately, we have no accurate information about 

 it from the physiologist. Such observations as have 

 been made relate to the part played by such ingredients 

 of weather as heat and moisture, and will be referred to 

 in another chapter. 



5. Of the influence of the nervous system on meta- 



* For a comprehensive study of the whole subject, see H. D. 

 Marsh, 'The Diurnal Course of Efficiency,' Archiv. of Phil. Psychol. 

 and Scientific Methods, No. 7, July, 1906 ; New York, Science 

 Press (abst. in Brit. Med. Journ., 1907, ii. 1541) 



