696 PHYSIOLOGY 



output of an average working man as 3000 Calories. It must be remem- 

 bered that this figure is only an average that is to say, it applies to a man 

 of average size and weight and doing a certain amount of work. A small 

 man will require less and a tall man more. A man in sedentary employ- 

 ment e. g. typewriting, clerking, etc. may not expend more than 200 to 

 400 Calories in the performance of external work; mental exertion causes 

 no appreciable rise in the metabolic exchanges. Such a man would there- 

 fore have a total energy output of not more than 2400 Calories a day. On 

 the other hand, a heavy worker, such as a navvy, may easily expend 2000 

 or more Calories a day in the performance of external work. It is not 

 surprising therefore that investigation of the diets actually in use among 

 different classes of men shows very wide divergencies. An examination of 

 the actual energy output as measured by the C0 2 excretion during work 

 gave the following approximate energy requirements for men in different 

 occupations : 



Occupation Energy Requirements 



Tailor 2500 



Bookbinder 2800 



Shoemaker 2850 



Metalworker .... 3200 



Painter 3250 



Carpenter 3200 



Stone mason .... 4400 



Woodcutter 5000 



The energy requirements of women will show corresponding variation 

 according to occupation, but will be in general less in consequence of their 

 smaller size and surface. Du Bois has shown that, in addition to the influence 

 of size, women have a lower basal metabolism per square metre of surface, 

 viz. 37 Calories per hour as against 40 in the case of men. The average 

 height and weight of Englishwomen are 159-3 cm. and 55-7 kilos, corre- 

 sponding to a surface of 1-511 square metres and to an hourly output of 

 56 Calories. In estimating the total energy requirements of an average 

 woman we may reckon her work as two-thirds that of a man, and as involv- 

 ing an expenditure of 660 Calories per day. We then arrive at the following 

 table for the energy requirements of the average woman : 



8 hours' sleep at 66 448 Calories. 



8 hours awake at 73 (Basal Metabolism plus 30 per cent.) 584 

 8 hours' work (Basal Metabolism plus 660 Cals.) . . 1108 



Total 2140 



It must be remembered that woman's work is rarely finished when she 

 goes home from her occupation, so that a certain amount ought to be 

 reckoned for housework. We shall not be far wroiiu tlion in accepting 

 the usual estimate of a woman's requirements as four-fifths of those of a 

 man, viz. 2400 Calories. Here again it must be remembered that this is 

 merely an average figure, and that the requirements of different women 

 correspond to their occupation and environment, and may vary from 1800 

 Calories up to 3000 Calories, or even more. 



