124 FOOD. 



scurvy. The green parts of vegetables are no doubt also useful by 

 furnishing to the system a supply of iron contained in their chlorophylle. 

 From what has been said above, it will be seen that the nutritious 

 character of any substance, or its value as an article of food, does not 

 depend simply upon its containing either one of the alimentary substances 

 in large quantity; but upon its containing them mingled together in 

 such proportion as is requisite for the healthy nutrition of the body. 

 What these proportions are cannot be determined from simple chemical 

 analysis, nor from any other data than those derived from observation 

 and experiment. 



Requisite Quantity of Food and of its Different Ingredients, 

 The entire quantity of food required per day varies with the circum- 

 stances of the individual, such as the size and weight of the body, the 

 comparative development of the muscular and other systems, the tem- 

 perature, and especially the amount of physical activity. More food is 

 required, on the average, in cold than in warm weather, more by persons 

 of a muscular than by those of an adipose or phlegmatic constitution, 

 more in a condition of active exertion than in one of comparative repose. 

 Even the proportion of different classes of proximate principles required 

 for nutrition varies to a considerable extent according to special condi- 

 tions. When the individual is in a perfectly healthy condition, and so 

 situated that he can supply himself at will with any kind of nourishment 

 desired, the natural demands of the appetite afford the surest criterion 

 for both the quantity and quality of the food to be used. But not 

 infrequently provision must be made in advance for supplies destined 

 to last over a considerable period, as in the case of military or exploring 

 expeditions, or for the inmates of hospitals or asylums where the diet 

 must be regulated to a great extent upon a uniform plan. It therefore 

 becomes important to know both the quantity and kind of food necessary 

 for the support of life. 



The standard adopted for this estimate is that of a healthy adult 

 man, employed in active but not exhausting occupation. The amount 

 requisite will be found to vary in either direction from this standard, 

 according to the circumstances above mentioned. The average require- 

 ments as given by different authors do not vary materially from each 

 other in any essential particular. According to our own observations, 

 a man in full health, taking active exercise in the open air, and restricted 

 to a diet of bread, fresh meat, and butter, with water and coffee for drink, 

 consumes the following quantities per day : 



QUANTITY OF FOOD REQUIRED PER DAT. 



Meat 453 grammes. 



Bread 540 



Butter or fat 100 " 



Water . 1530 



This represents the requisite daily quantity of food and the propor- 

 tions of its different kinds, when composed of such articles as are most 



