184 



THE ENERGY OF THE LIVING PROTOPLASM. 



platinum-black, which renders the alcohol molecule so labile that 

 it readily takes up oxygen. We must look upon both kinds of 

 phenomena as katalytic oxidations (cf. the foregoing chapter). (I) 



It is the CH, — group in the fatty acids and amido acids, 

 and the CH OH — group in ketoses, aldoses, and hydroxylated 

 acids that are most easily attacked. The carboxyl-group renders 

 the CH OH — group in a molecule much more easily attackable 

 than does the alcoholic group CH 2 OH. Thus, we see that 

 glycerol and mannitol are (at least in the animal) by no means 

 easily oxidised, while, e.g., tartaric acid is. The influence of the 

 carboxyl-group also becomes evident when we compare the 

 bibasic phthalic acid with the monobasic benzoic acid ; the 

 latter resists while the former is for the greater part burned up. 

 That in the animal the amido-acids (leucin, glycocoll, tyrosin) 

 undergo combustion with especial facility, yielding thereby urea 

 was demonstrated by Ncncki and Schultzen, as early as 1872, and 

 later on by Knicricm, Schmicdcbcrg, Wciske, and Lewinsky, in 

 experiments with asparagin. Ncncki declared, therefore, the amido- 

 compounds to be the forerunners of urea. {1) This view, which does 

 not assume a direct oxidation of dissolved proteids, but a pre- 

 vious splitting into a group of well known amido-acids, is very 

 well supported by observations of Hofmcistcr, which prove with 

 what difficulty peptone, as such, is oxidised in the living animal. 

 A rabbit of 1.75 kilo, in weight, discharged, after intravenous injec- 



(1) Nencki and Siebcr have tried to determine the extent of oxidation which 

 sugar and albumin can undergo if exposed at 36" in alkaline solution to air, and have 

 found it to be very slight. How little the protoplasm itself participates directly in 

 the oxidation process may be illustrated by the fact that 95 per cent of the matter 

 oxidised may be sugar and only 5 per cent proteids ; with bees the percentage of 

 the latter is still less. 



(2) The amido-acids from proteids are even more quickly oxidised in the cells 

 than the carbohydrates, as must be concluded from investigations by Kumagaiva, 

 who nourrished dogs with an excess of lean meat and observed that under this con- 

 dition also the glycogen of the meat was deposited as fat in the animal (Mittheilun- 

 gen der medic. Facultat, Tokyo). It is, moreover, of great interest to observe how 

 the production of urea is influenced by the chemical constitution : negative groups 

 connected with the nitrogen will prevent the formation of urea, as Nencki has shown 

 with acetamide, recalling the resistance of hippuric acid. But taurin and sarkosin 

 are also oxidised with difficulty, reappearing as uramido compounds in the urine 

 (Salkowski). Urea must be considered as a synthetical product from carbamic acid 

 and ammonia (Drechsel and Abel ; Ncncki and Hahn). 



