452 POPULAR SCIENCE MONTHLY. 



whatever the age of the individual exposed ; and no less against diseases 

 not attributable to germs — and the more if we accept Metschnikoff's 

 theory of the office of the leucocytes or white blood corpuscles, for 

 these in both number and strength depend upon proper nourishment. 

 'In health/ says Kirke, 'the proportion of white to red corpuscles, 

 which, taking an average, is about 1 to 500 or 600, varies considerably, 

 even in the course of the same day. The variations appear to depend 

 chiefly on the amount and probably also on the kind of food taken, 

 the number of leucocytes being very considerably increased by a meal, 

 and diminished again on fasting. Also in young persons, during 

 pregnancy, and after great loss of blood, there is a large proportion 

 of colorless blood corpuscles, which probably shows that they are more 

 rapidly formed under these circumstances. In old age, on the other 

 hand, their proportion is diminished.'* 



No good observer will fail to recognize the coincidence of the con- 

 dition which diminishes the proportion of leucocytes and the increased 

 liability to disease — that of fasting; or note the no less remarkable 

 coincidence, the diminution in the number of leucocytes and increas- 

 ing infirmity of old age. 



Foods are ordinarily divided into four classes: (1) Nitrogenous or 

 albuminous substances; (2) fats or hydrocarbons; (3) carbohydrates, 

 chiefly starchy substances and sugar; (4) mineral substances — water 

 and salts. 



The average daily amount of food required and of the different 

 kinds, as comprehended in this classification, severally, varies con- 

 siderably with individual conditions of age, size, exercise, circulation, 

 activity of the eliminating organs, etc. The range in different male 

 adults is from 34 to 46 ounces of so-called solid food, and from 70 to 90 

 ounces of water in some form, taken with and without solid food. For 

 adult females, the average is from 3 to 5 ounces less. For children 

 and youths, proportionally, more in the inverse ratio to age, 0.8 to 0.6 

 ounces for each pound weight of the body. 



If individuals are undergoing great exertion they require more 

 food, and, if they can obtain it, the needful increase is especially in the 

 nitrogenous and fat foods. 



Every structure in the body in which any form of energy is manifested 

 (heat, mechanical motion, chemical or electric action, etc.) is nitrogenous. The 

 nerves, the muscles, the gland-cells, the floating cells in the various liquids, 

 the semen, and the ovarian cells, are all nitrogenous. Even the non-cellular 

 liquids passing out into the alimentary canal at various points, which have so 

 great an action in preparing the food in different ways, are not only nitrog- 

 enous, but the constancy of this implies the necessity of the nitrogen in order 

 that these actions shall be performed ; and the same constancy of the presence of 

 nitrogen, where function is performed, is apparently traceable through the 

 whole world. Surely such constancy proves necessity. (Parkes.) 



* Kirke's ' Hand-Book of Physiology,' Vol. I., p. 79. 



