488 PHYSIOLOGY. 



Sulphur. This is furnished especially by the vegetable and 

 animal proteids. A certain proportion exists between the total nitro- 

 gen and the total amount of sulphur excreted, as proteid metabolism 

 furnishes both. For one gram of sulphur, fourteen to sixteen 

 grams of nitrogen are excreted. 



Iron. Such compounds of iron as are contained in nuclein found 

 in the yelk of egg have been termed by Bunge, hcematogens. In the 

 chick the developing red corpuscles obtain their iron from it. Iron is 

 absorbed through the duodenum and excreted mainly through the 

 mucous membrane of the colon. Inorganic and organic combinations 

 of iron are absorbed. Iron is deposited in lymph-ganglia, spleen and 

 liver. 



The Aim of Alimentation. 



Alimentation has for its end (1) to furnish materials for 

 catabolism, and (2) to furnish suitable products for anabolism. That 

 is, to replace and rejuvenate the organized substances which are 

 destroyed in the former process. 



To know what are the foods which the body needs, it becomes 

 necessary to study the substances which undergo anabolism and 

 catabolism. It is these substances which must enter into our daily 

 nourishment. These two processes ensue in all of the substances, 

 without any exception, which compose the organism. Hence, all the 

 principles of which the economy is composed are indispensable in 

 food : water, proteids, fat, carbohydrates and salts. 



Foods. Each one of these principles taken in an isolated manner 

 is not a complete food, since it is not able to replace its neighbor. 

 Thus, water is as necessary a food as is proteid, but yet water is not 

 a complete food. 



A food is any product which is capable of being transformed into 

 a proximate principle of the organism, or capable of at least diminish- 

 ing or preventing the destruction of this principle. Hence, a 

 complete food is the sum of the food-products capable of preserving or 

 augmenting the sum of the proximate principles of which the organism 

 is composed. 



The fundamental principles which enter into the chemical com- 

 position of the human body water, proteids, fats, carbohydrates and 

 salts are in themselves composed of simple elements: 0, H, C,,S, N, 

 P, Cl, K, Na, Mg, Fe, silicon and fluorin. 



Will these simple elements, upon ingestion, become converted into 

 complex principles and so constitute foods? 



They will in the case of the plant, for it is able to form a complex 



