I.— PHYSIOLOGY. 



167 



rise ten times. 'J'hus llio subject studied by Benedict and myself liad 

 a normal consumpt of about 20U c.c. oxygen per minute, and in one 

 experiment he kept up an intake of nearly 2,0LK) c.c. per minute for 

 four hours and twenty-two minut-es on end. Quite often the same 

 subject used 2,700 c.c. to 3,000 c.c. for ten minutes at a time. Again, 

 at rest less than a third of the oxygen present in the blood is required, 

 and even in the very hardest work the arterial blood is not depleted of 

 its oxygen ; it probably still contains more than a fourth. Curiously 

 enough, the actual effectors, the muscles, do not of themselves seem 

 to have a very high factor of safety. The structures, bones, and carti- 

 lage, tO' which they are attached, and which limit their action, and 

 the amount of strain to which they can be exposed or subjected, have 

 a very high factor of safety. A further protective mechanism for 

 muscle is the perfect co-ordination between the groups of muscles, the 

 elucidation of which problem we owe largely to our President, Sir 

 Charles S. Sherrington. "We have another reserve of first-class im- 

 portance — viz., that when the strain on one group of muscles is be- 

 coming too severe, more and more groups of muscles are brought 

 into action to help in meeting the strain, until in the end, if need be, 

 practically the total musculature of the body is involved. And behind 

 all this there are final factors of safety such as fatigue, which is a 

 protective warning; and finally, if the latter be not heeded, collapse. 

 This perfect co-ordination of the different parts of the organism is 

 required, because the human being is capable of intense muscular exer- 

 tion for short periods. The intensity of the work is as a general rule 

 inversely proportional to the length of time during which it must be 

 carried out. The following table (Table I.) gives some idea of what is 

 probably about the maximum effective muscular work per minute 

 (modified from Blix) : — 



Table I. 



If, in the human organism, we were merely concerned with the co- 

 ordinated action of a series of effectors, with the capacity of a certain 

 group of muscles to perform a given amount of work, the solution 

 of the problem would be relatively simple But we are dealing with 

 a living organism capable not only of doing work but oi repairing tfie 

 worn-out parts as and when required. Further, we are dealing with 

 an organism which varies not only in its capacity to perform work, 

 but in its ' will to work. ' We are dealing with a subtle organism which 



