I.— Plli'SlOLOGY. 175 



that supplies of material are not constant, or that, if these more or less 

 natural conditions do not operate, rests at irregular intervals are 

 deliberately taken liy the operative. 



So far as I am aware there is only one type of hard work where 

 a definite rest period is laid down as part of the exercise, namely, in 

 Army route marching. Marching as a costly form of energy expendi- 

 tui'e is unique in that it is a continuous repetitive act carried on 

 frequently for hours on end. The Regulations lay down that a definite 

 rest period shall be taken every hour. Marching, too, is peculiar in 

 another way, namely, that the rate of marching is fixed, i.e. a certain 

 definite rate has to be constantly maintained throughout the marcliing 

 period. 



It can be shown that if a certain distance has to be covered in a 

 definite time there is an optimum rate of forward progression. Cathcart, 

 Lothian, and Greenwood found, for example, that when the cost per 

 mile alone was considered, the minimum value was reached at a rate of 

 about three miles per hour, but when the question of time as well as 

 distance arose, i.e. if a distance of, let us say, one mile was to be covei'ed 

 and sixty minutes were available to do it in, would it be more economical 

 to march the mile rapidly or slowly and have a longer or shorter pei'iod 

 of rest? Our experiments showed that the lowest hourly value was 

 obtained at a rate of a mile in about twenty-three minutes, i.e. marching 

 for twenty-three minutes in the hour and resting for thirty-seven minutes. 

 To spend thirty-two minutes on the march cost about 5 per cent, more, 

 and to reduce the marching time to sixteen minutes increased the cost 

 by about 15 per cent. 



So much, then, for the ordinary effector factors. There are many 

 other factors directly concerned with the efficient action of the organism, 

 some directly influencing the internal economy of the bodv. others 

 acting more indirectly on the organism from the environment. 



One of these factors is the state of the nutrition. It may be 

 definitely stated that an insufficient intake of food or the consumplion 

 of poor or inadequate food is one of the chief sources of general in- 

 efficiency. Our resistance to the effects of hard and continual work. 

 just as to the effects of an infection, is largely controlled by our re- 

 serves. The capacity of the body to store reserve food material which 

 will meet the daily demands for energy and leave a surplus is another 

 of the vital factors of safety. The body is undoubtedly capable of with- 

 standing complete deprivation of food for comparatively long periods, 

 but with a corresponding depression in its capacity to perform external 

 work. Complete starvation is a state which is rare, and does not 

 affect the question at issue. The much more important problem is un- 

 fortunately only toO' common, the influence of chronic undernutrition, 

 a condition which lowers efficiency, not merely in the actual perform- 

 ance of muscular work, but by inducing an increased susceptibility to 

 disease. This is a question which has never received the attention 

 whicli its importance demands, largely on account of the immense 

 diffirulties of carrying O'ut the investigation in a practical manner. As 

 the direct result of the war we have the records of at least two sets 

 of oliserxers. Benedict and his eo-workcrs in\i's(igaled llu> prnl)K>tn. 



1922 u 



