THE MUTUAL RELATIONS. 309 



nating rape-seeds. If we permit these to develop away from the light, we 

 observe the fat disappearing from the cotyledons. In its place we find 

 carbohydrates: starch, cellulose, gum, sugar. If we allow seeds, rich in 

 starch, to germinate in glass tubes sealed under mercury, no change in the 

 volume of gas can be observed. During the germination of seeds contain- 

 ing oil, on the other hand, we notice that gas is being consumed, from 

 the fact that the mercury rises. This corresponds to the amount of 

 oxygen which is required to convert the fats into carbohydrates which are 

 richer in oxygen. These important observations were made by Julius 

 Sachs and Wiesner 1 in 1859. 



There is, therefore, no doubt that the plant cell is capable of pro- 

 ducing carbohydrate from fat, and, conversely, fat from carbohydrate. If 

 we assume with Kassowitz 2 that the protoplasm absorbs, or assimilates, 

 one of these compounds, e.g., the fat, in order subsequently to form 

 in this case, the carbohydrate, in such a way that there is no direct con- 

 nection between the two compounds, then we miss the point at issue, and 

 the whole process is beyond our understanding, for it cannot be a matter 

 of indifference for the functions of the protoplasm, whether at one time 

 fat, at another time carbohydrate, and yet again albumin, is at its disposal. 

 The question concerning the transformations of the separate food-stuffs 

 is only postponed by such assumptions, and it becomes more involved and 

 obscure. 



A much disputed question is this : Does the animal cell possess the same 

 abilities as the plant cells? Can the animal organism convert fats into 

 carbohydrates, and, conversely, carbohydrates into fats? The last ques- 

 tion has been answered in the affirmative. We know that with a diet 

 rich in carbohydrates, an appreciable part of the ingested carbohydrate 

 is not stored up in the form of glycogen, although there is no glucohemia. 

 The fact forces us to the conclusion that carbohydrates can be stored away 

 as reserve material in some other form than glycogen. Numerous feeding 

 experiments have shown that an accumulation of fat follows a diet com- 

 posed largely of carbohydrates. 3 This decision may be reached in two 

 different ways: first, by determining the amounts of fat formed with 

 a diet containing a definite quantity of fat, albumin, and carbohydrate; 

 and secondly, by estimating the daily elimination of carbon dioxide. The 

 first proof has been carried out, as a rule, in the following manner: Two 



1 J. Sachs: Bot. Zeit. 1859. 



3 Cf. M. Kassowitz: Allgemeine Biologic (3 vols.). 



3 Cf. also B. Schulze: Landw. Jb. 1, 57 (1882). F. Soxhlet: Z. Landw. Vers. Bayern. 

 August (1881). St. Chaniewski: Z. Biol. 20, 179 (1884). H. Weiske and E. Wild: 

 ibid. 10, 1 (1874). I. Munk: Arch. Path. Anat. 101, 91 (1886). E. Meissl and F. 

 Strohmer: Sitzber. Akad. Wiss. Berlin, 88, HI (July, 1883), and Monatsh. 4, 801 (1883). 

 E. Meissl, F. Strohmer, and N. v. Lorenz: Z. Biol. 22, 63 (1886). C. Voit: Sitzungsber. 

 Miinchener Akad. 1886, p. 288. M. Rubner: Z. Biol. 22, 272 (1886). 



