156 POPULAR SCIENCE MONTHLY. 



added field of inquiry, worthy of careful consideration, if we are to 

 possess a clear understanding of nature's processes. 



Between the animal and the vegetable cell certain sharp lines of dis- 

 tinction are frequently drawn. Physiologists are wont to believe that 

 the processes characteristic of the cells of animal tissues and organs are 

 essentially destructive, i. e., that they are principally katabolic, while in 

 vegetable tissues, on the other hand, constructive processes are very 

 conspicuous. In no way is this better illustrated than in the prevalent 

 opinions regarding the parts played by the two classes of cells in the 

 metabolism of proteid matter. We are accustomed to think that all 

 proteid matter has its primary origin in the synthetical power of the 

 vegetable cell, aided by its contained chlorophyll and the beneficent 

 action of the sun's rays. The animal cell, on the other hand, can 

 merely transform and reconstruct the various proteids furnished by 

 the vegetable world, being without power to manufacture proteid matter 

 dc novo out of the simple groups and radicles which the vegetable cell 

 utilizes so rapidly. In ordinary proteid katabolism, the various nitrog- 

 enous decomposition products are presumably all converted into urea 

 and allied substances adapted for excretion. If, however, there is 

 reversible ferment or enzyme action in the animal body, why may there 

 not also be power to utilize, in some measure at least, the crystalline 

 nitrogenous bases and amido-acids so abundantly formed in trypsin 

 proteolysis, for the construction of fresh proteid matter ? One may well 

 query, considering the vigor of the proteolytic action of the enzymes 

 poured into the alimentary tract, whether all these nitrogenous waste 

 products represent just so much lost energy in their production and a 

 further loss of energy in their immediate excretion from the body. In 

 harmony with the ' luxus consumption ' theory we may assume wisdom 

 and ultimate gain in this speedy decomposition of excessive proteid 

 foods in the alimentary tract, but the argument is not very convincing. 

 Why may not animal cells, or the animal body as a whole, build up 

 proteid matter out of simple nitrogenous compounds analogous to the 

 action of plant cells ? Loewi* has indeed experimented in this direction 

 and states that the biuret-free end-products resulting from the pro- 

 teolysis of ordinary food albumin can be utilized by the animal body 

 for the maintenance of nitrogenous equilibrium, etc., equally well with 

 the common proteid food-stuffs. His conclusions, however, have been 

 called in question by other investigators, notably by Lesserf whose ex- 

 perimental data failed to confirm the above conclusion. 



The problem, however, is an exceedingly important one. If the 

 animal body has no power of utilizing the varied nitrogenous com- 



* ' Ueber Eiweissynthese im Tbierkorper, 5 Archiv fur exper. Pharmakol. u. 

 Pathol, Band 48, p. 303. 



t ' Ueber Stoffwechselversuehe mit den Endprodukten peptischer und 

 tryptischer Eiweissverdauung,' Zeitsclir. filr Biologic, Band 45, p. 497. 



