36 BIOLOGICAL PROBLEMS 



processes of digestion. Each pair of figures refers to 

 a separate individual, the same in each case. 



It will be seen that the second bread proved, as a 

 matter of fact, to be slightly less digestible than the 

 first, but a simple calculation will show that this 

 decrease in digestibility is not nearly sufficient to out- 

 weigh the gain in food yielded by the more complete 

 extraction of the wheat. The authors of the report 

 calculate, after allowing for the smaller digestibility, 

 and also for the fact that the appearance of more of 

 the wheat grain in bread diminishes the amount avail- 

 able for feeding animals, that a substantial gain to 

 the national larder results from the higher standard 

 of milling. The difference between 80 and 90 per 

 cent extraction increases the supply of energy derived 

 from the year's supply of cereal food to an extent 

 which will cover a month's consumption. 



The amount of energy made available is the most 

 useful datum for practical guidance when such ques- 

 tions arise, but the Royal Society's experiments deal 

 further with the protein supply, and show that the 

 nation also gains in this as a result of the higher 

 extraction of its wheat. 



In a second part of the report experiments are 

 described showing the availability of the energy and 

 protein contained in a bread at 8o-per-cent extraction, 

 in which the wheat was mixed with 20 per cent of 

 maize. It was tested upon the same individuals as 

 before, but also upon five additional subjects making 

 seventeen in all of whom four were children. The 

 average digestibility of a diet comprising this bread 

 was exactly that of one containing the all-wheaten 

 bread at 8o-per-cent extraction. 



A third part of the report describes the effect of 

 similar bread containing mixed cereals upon the 

 appetite and health of invalids at sanitoria and of a 



