THE INFLUENCE OF INTERNAL FACTORS 65 



kilogram and minute went down 14 per cent In female dogs the 

 effect of castration took a longer time to develop, but the metabolism 

 finally went down from 6*1 6 c.c. of oxygen per kilogram and minute 

 to 5 '05 c.c. (20 per cent). There was an increase in weight, but a 

 decrease in absolute metabolism amounting to 9 per cent Ovarial 

 substance, which had no effect on normal dogs, produced in the cas- 

 trates, both male and female, a very considerable increase in the 

 standard metabolism. Leo Zuntz [1908] observed a decrease in meta- 

 bolism in some cases of extirpation of the ovaria in women, but the 

 results were not constant. The change took place after a considerable 

 interval of time. 



Liithje[i9O2], who selected two young male dogs and two females, 

 all from the same litter, and castrated one of each sex, did not observe 

 any distinct difference between the castrates and the controls in the 

 respiratory exchange (carbon dioxide determined in 24-hour periods) 

 though he continued his observation over several years. As shown 

 in the criticism by Loewy and Richter [1902] his method would not 

 be likely to give trustworthy evidence with regard to standard meta- 

 bolism. 



A priori it would appear perfectly natural to expect that certain 

 hormones should be able to stimulate the oxidative energy of the 

 tissues, acting as catalysers, but the experimental evidence in favour 

 of the process must in the writer's opinion be regarded as inconclusive. 



Experiments on the influence of internal factors upon standard 

 metabolism have so far been made only on mammals, and while their 

 correct interpretation even for this class 'of animals is doubtful, it 

 would be hazardous to attempt any conclusion for the whole animal 

 kingdom. In Chapter VIII, section 3, various observations and re- 

 searches will be mentioned, which suggest that the standard meta- 

 bolism in certain lower animals may be variable within wide limits 

 independently of all external influences. 



