PRESENT PROBLEMS 341 



have an 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 pre- 

 valent 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 bene- 

 ficent 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 pow r er to manufacture proteid 

 matter de novo out of the simple groups and radicles which the vege- 

 table cell utilizes so rapidly. In ordinary proteid katabolism, the 

 various nitrogenous decomposition-products are presumably all con- 

 verted into urea and allied substances adapted for excretion. If, how- 

 ever, 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 de- 

 composition 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? Loew * 

 has indeed experimented in this direction and states that the biuret- 

 free end-products resulting from the proteolysis 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 Lesser, 2 whose experimental 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- 



1 Ueber Eiweissynthese im Thierkorper, Archiv fiirexper. Pharmakol. u. Pathol., 

 Band 48, p. 303. 



2 Ueber Stoffwechselversuche mil den Endprodukten peptischer und tryptischer 

 Eiweissverdauung, Zeitschr. fur Biologic, Band 45, p. 497. 



