DIETETICS 633 



peripheral nerves (peripheral neuritis) and consequent paralysis, has 

 greatly increased among the rice-eating Japanese, in Bengal, although 

 much rice is eaten, there is practically no beri-beri, as country rice and 

 not the highly polished variety is consumed. When birds e.g. : 

 pigeons are fed on polished rice, polyneuritis similar to that seen in 

 human beri-beri is produced, and both in man and in birds the condi- 

 tion is quickly cured by reverting to rice prepared according to the 

 old-fashioned methods, or by adding the polishings or an alcoholic 

 extract of them containing the essential substance, or the isolated 

 base itself. 



The addition of various legumes to the diet, or alcoholic extracts 

 of these, will produce the same beneficial effect (McCay). Potatoes, 

 carrots, fresh vegetables, lime and other fruit juices, also certain 

 animal foods, such as fresh milk, fresh meat, and yolk of egg, are 

 all valuable, in addition to their ordinary nutritive constituents, for 

 their content of vitamines. Yeast contains them in exceptionally 

 large amount, and it is possible, though not proved, that such fer- 

 mented liquors as beer, or some varieties of it, may derive some part 

 of their value from these substances liberated both from the yeast 

 and the barley and not destroyed in the process of brewing. 



The addition of yeast to artificial diets accelerates the growth of 

 young rats. Yeast also prevents and cures polyneuritis developed in 

 birds by a diet of polished rice. It is not known whether the growth- 

 promoting component is identical with the anti-neuritic one or a different 

 substance. 



Since vitamines exert so great an effect on nutrition and growth, 

 it might be expected that their absence would tell on those glands 

 of internal secretion which appear to be concerned in the metabolism 

 of growth. As a matter of fact, it has been found that in pigeons 

 suffering from the typical deficiency disease beri-beri, certain of these 

 glands show marked changes. The thymus gland, normally very 

 large and persistent in these birds, can be caused to atrophy com- 

 pletely by a diet of polished rice. Changes also occur in the 

 pituitary, and decided atrophy in the testes and ovaries (Funk and 

 Douglas). 



In bringing this chapter to a close, it may be useful to point out 

 again that indispensable as the data of physiology are for intelligent 

 and fruitful criticism of the dietetic habits of individuals or communi- 

 ties, they must be applied with due regard to the other factors. 

 Nothing is more sure than that a certain minimum number of calories 

 must be supplied to an average man of given weight and age, living 

 and working under definite conditions, in order that his body may 

 be maintained in health. It is also well made out that a certain 

 balance, which, however, is by no means rigidly fixed, between the 

 great groups of food-stuffs is of the essence of a good dietary. Yet 

 of two rations each containing the proper number of calories, and 

 the conventional proportions of protein, carbohydrate and fat, one 

 may be good and sufficient, and the other so gravely deficient that 

 malnutrition or disease may follow the use of it. Where natural 

 foods are obtainable in abundance and variety, there is seldom 

 danger of a lack of the indispensable accessories. This danger in- 

 creases when economic or social conditions lead to an excessive use 



