NITROGENOUS ALIMENTARY SUBSTANCES 143 



ALIMENTATION 



Under the name of aliment, in its widest signification, it is proposed 

 to include all articles composed of or containing substances in a form 

 in which they can be used for the nourishment of the body, either by 

 being themselves appropriated by the organism, by influencing favorably 

 the processes of nutrition or by retarding katabolism. The substances 

 that are themselves appropriated may be called direct aliments; and 

 those which simply assist nutrition without contributing reparative mate- 

 rial, together with those which retard katabolism, may be termed indi- 

 rect aliments. In this definition of aliment, nothing is excluded that 

 contributes to nutrition. Oxygen must be considered in this light, as 

 well as water and all articles commonly called drinks. 



In the various articles used as food, nutritious substances frequently 

 are combined with each other and with indigestible and innutritious 

 matters. The constituents of the food directly used in nutrition are the 

 true alimentary substances, embracing, thus, only those capable of ab- 

 sorption and assimilation. The ordinary food of warm-blooded animals 

 contains alimentary matters united with innutritious substances from 

 which they are separated in digestion. This necessitates a complicated 

 digestive apparatus. In some of the inferior animals, the quantity of 

 nutritious matter forms so small a part of the ingesta that the digestive 

 apparatus is more complicated than in the human subject. This is 

 specially marked in the herbivora, the flesh of which is an important 

 part of the diet of man. In addition to what are distinctly recognized 

 as alimentary substances, food has many constituents that exert an im- 

 portant influence on nutrition, which have never been isolated and 

 analyzed, but which render it agreeable. Many of these are developed 

 in the process of cooking. 



Alimentary substances belong to the inorganic, vegetable and 

 animal kingdoms. They may be divided into the following classes : 



1. Organic nitrogenous substances (albumin, fibrin, casein, myosin 

 etc.), belonging to the animal kingdom, and vegetable nitrogenous sub- 

 stances, such as gluten and legumin. 



2. Organic non-nitrogenous substances (sugars, starch and fats). 



3. Inorganic substances. 



Nitrogenotis Alimentary Substances. In the nutrition of certain 

 classes of animals, these substances are derived exclusively from the 

 animal kingdom, and in others, exclusively from the vegetable kingdom; 

 but in man, both animals and vegetables contribute nitrogenous matters. 

 In both animal and vegetable food, nitrogenous substances are always 

 found associated with inorganic matters (water, sodium chloride, the 



