354 LECTURE XVI. 



cells must also be included. As we have said, water and inorganic salts, 

 neither of which imparts to the organism any chemical energy, must neces- 

 sarily be considered as foods, for they exercise this function of being of 

 use to the cells. Now we know that the animal organism takes up a 

 considerable amount of salts with its food, while on the other hand it is 

 equally well known that the organism constantly eliminates salt in the 

 urine and in the sweat. These losses must naturally be replaced. For 

 the salts it would seem, a priori, as if there were not much need for such 

 replacement. We could easily imagine that the salts set free in the break- 

 ing down of cell-material could be used anew in the formation of new cells. 

 With water it is quite another matter, because the organism needs water 

 for a number of different processes. Its importance is shown by the fact 

 that two-thirds of the animal organism consists of water. Every cell 

 must contain water. It forms one of the prime conditions for a definite 

 physical consistency of the cell. Water is absolutely necessary as a 

 solvent for numerous compounds. It brings into play numerous chemical 

 reactions, and takes part in the building up and breaking down of sub- 

 stances without number. It is a carrier of nourishment to the body, 

 whether through the blood, the lymph, or the finest fissures between the 

 cell; and, conversely, it provides the means for carrying away the waste 

 products. When we remember in addition that the body must give up 

 water to the air in the process of respiration, and that in water the animal 

 organism possesses its most important means of regulating the temperature 

 of the body, by virtue of its evaporation on the surface, it soon becomes 

 apparent why water plays such an all-important part in the life process 

 not only for animals but naturally for plants as well. In the combustion 

 of the food, naturally some water is formed in the body, but this amount 

 is so small that it by no means suffices to satisfy all the requirements. 

 The animal organism must have a supply of water from without. 



Now, are the inorganic salts also indispensable for the nourishment of 

 the fully developed organism? An attempt has been made to answer 

 this question by providing animals with food which is as free from ash as 

 possible. The first to perform such experiments was Forster. 1 As food 

 he made use of the meat residue obtained in the preparation of Liebig's 

 Extract of Beef. After having been repeatedly boiled with water, such 

 meat contains only 0.8 gram of ash, for each 100 grams of dry substance. 

 This, together with fat, sugar, and starch, he fed to two dogs. Both of 

 the animals experimented upon died very soon; in fact, much more quickly 

 than if they had not been fed at all. The same result was obtained by 

 feeding three pigeons with starch and casein. Against the conclusion 

 that death was caused by lack of salt, G. von Bunge 2 very properly raised 



1 Z. Biol. 9, 297 and 369 (1873). 



2 Ibid. 10, 111 and 130 (1874). 



