PHYSIOLOGY OF METABOLISM. 



SCOPE OF METABOLISM. 



By metabolism is understood the phenomenon common to all living 

 organisms, sharply differentiating the organized from the unorganized, 

 and consisting in the power of incorporating into their own tissues 

 the substances obtained from food (in animals by means of digestion) 

 and of forming them into component parts of their own animate 

 bodies. This division of metabolism is designated assimilation. More- 

 over, out of these assimilated substances, which constitute a reservoir of 

 potential energy, the organism is, by means of transformation-processes, 

 able to develop activities in the form of kinetic energy, which are mani- 

 fested most strikingly among the higher animals as muscular work and 

 heat. The resulting transformation of tissue-constituents, which ter- 

 minates in the formation of excrementitious substances, is thus an in- 

 direct object in the study of metabolism. 



Normal metabolism requires, accordingly, food-material suitable 

 both qualitatively and quantitatively; a storing up within the body, in 

 proportion to the consumption ; a regulated chemical transformation of 

 the tissues ; and the preparation of the waste-products to be thrown off 

 by the organs of excretion. 



SYNOPSIS OF THE MOST IMPORTANT SUBSTANCES 



USED AS FOOD. 



WATER. EXAMINATION OF DRINKING-WATER. 



When it is considered that the body contains in all of its tissues about 58.5 

 per cent, of water, that water is constantly being thrown off with the urine and 

 the feces, as well as by the skin and the lungs, and that in the processes of digestion 

 and absorption most substances must be dissolved in water, and likewise that 

 numerous waste-products, especially in the urine, must leave the body in aqueous 

 solution, the importance of a constant supply and continual renewal of water will 

 be at once obvious. Hoppe-Seyler epitomized admirably the importance of water 

 to life in the following words: "All organisms live in water, and indeed in running 

 water," a saying that deserves a place by the side of the old one of "Corpora non 

 agunt nisi fluida." 



Leaving out of consideration its presence as a constituent of fluid food, water 

 is used as a drink in different forms: (i) As rain-water (in some countries, where 

 it is collected in suitable reservoirs, cisterns, etc.) , which most closely approximates 

 distilled (chemically pure) water, although it, nevertheless, always contains small 

 amounts of carbon dioxid, ammonia, nitrous and nitric acids. (2) As well-water or 

 spring-water, which is ordinarily rich in mineral matter, it results from atmos- 

 pheric precipitations, which filter through the layers of earth rich in carbon dioxid, 

 and with the aid of the absorbed carbon dioxid it is capable of dissolving out 

 the alkalies, the alkaline earths and metals. These substances enter into solution 

 as bicarbonates, for instance calcium carbonate and ferric carbonate. The water 

 is either drawn from the wells by mechanical appliances or it gushes from the 



