164 GENERAL PHYSIOLOGY 



contents in the latter than in the former. This experiment proves 

 that fat must actually have arisen in phosphorus poisoning. Franz 

 Hofmann ('72), however, performed an experiment which showed 

 directly the origin of fat from proteid. He took a quantity of eggs 

 from the bluebottle fly (Mtisca vomitoria) and divided them by 

 weight into two equal portions. One of these portions he em- 

 ployed for the determination of the fat-contents, the other he laid 

 upon blood, the small quantity of fat contained in which was like- 

 wise determined. The larvse of the flies creeping out of the eggs 

 fed upon the blood and grew. After they were grown, Hofmann 

 determined the quantity of fat in them, and found that they con- 

 tained ten times as much fat as the eggs and the blood together. 

 On account of its minute quantity, the blood-sugar need not 

 be considered in the fat-formation. Hence the fat could have 

 come only from the proteid of the blood. After these experiments 

 it is no longer doubtful that fat can originate from proteid. 

 Neither can doubt exist concerning the origin of carhohydratcs 

 (grape-sugar and glycogen) from proteid. It has been known for 

 a long time that in severe forms of diabetes mellitus, even with 

 complete lack of carbohydrates in the food, the quantity of grape- 

 sugar excreted in the urine is considerably increased by the 

 consumption of an increased quantity of proteid. Likewise, 

 Claude Bernard has observed that in dogs in which the glycogen 

 had been used up by fasting, glycogen is stored in greater quan- 

 tity when they are fed abundantly upon pure proteid food ; and in 

 a dog that had been fed for four days with pure fibrin after fasting 

 twenty-one days, Mering ('77) found more than sixteen grams of 

 glycogen in the liver. Numerous similar observations have been 

 made, and the origin of carbohydrates from proteids is now assured. 

 The origin of lactic acid from proteid has been proved by the 

 investigations of Gaglio ('86), which show that the lactic acid of 

 the blood depends only upon the quantity of ingested proteid, not 

 upon that of the carbohydrates. Finally, that carbonic acid also, 

 which all living substance without exception expires throughout 

 its life, is derived from the decomposition of proteid and not from 

 that of non-nitrogenous substances, is at once evident from the 

 fact that in carnivora life can be maintained continually with 

 proteid food alone. This important fact proves in general that 

 from proteid all those substances can be formed that are continu- 

 ally excreted by the organism, as well as all the substances that 

 are necessary to maintain life. 



Formerly a sharp distinction was drawn between animal- and 

 plant-cells as regards the kind of chemical transformations that 

 take place in them. It was said that in the plants synthetic 

 processes take place almost exclusively, in the animals analytic 

 processes only ; and this idea has persisted until recent times. But 

 that such a fundamental difference exists was energeticalljr dis- 



