170 PHYSIOLOGY OF NUTRITION 



3. Enzymes in dead cells are destroyed by various poisons and bacteria, that 

 have no effect upon them in the living cell. Korsakova 1 showed that living yeast 

 cells exhibit alcoholic fermentation in the presence of considerable amounts of 

 sodium selenite, but the production of carbon dioxide in yeast killed with ace- 

 tone is stopped at once by a trace of this substance. 



The experiments described above show that life-processes are not to be inter- 

 preted simply as enzymatic activity. Enzymatic activities are regulated in 

 living cells, and the apparently unregulated processes carried out by the enzymes 

 of dead cells indicate that enzymes really play a subordinate role in the life of the 

 organism. 



Living protoplasm is not to be considered merely as a complex of heterogene- 

 ous enzymes. Enzymes are, in a manner of speaking, workers in the service 

 of the protoplasm; they are formed by the protoplasm, used in the work that is 

 in hand, and then imprisoned or destroyed as soon as their activities are no 

 longer required.' Enzymes that have become unnecessary are rendered inactive 

 by specific anti-enzymes; they are imprisoned, as it were, and when they once 

 more become necessary they are rendered active again, from the condition of 

 proenzymes, by activators or kinases. Activators or kinases on the one hand, 

 and anti-enzymes on the other, are thus the agents through which the regulating 

 power exerted by the protoplasm is effected. 



In the animal organism, moreover, special substances are found that not 

 only modify the activities of the various enzymes but also regulate the processes 

 of the whole body, and even initiate the development of new organs. These 

 substances arise in some particular organ and then migrate into far-distant 

 regions, where they set up whole series of definite chemical reactions. Such 

 chemical messengers have been called hormones by Starling. 2 



§4. Protein Decomposition in Plants.'" — As has been stated above, proteins 

 do not remain unchanged in plants, but are continually being broken down and 

 again reformed. 3 Some life-processes depend upon protein decomposition and 

 others upon protein synthesis. Etiolated seedlings and actively growing plant 

 organs are very satisfactory subjects for the study of protein decomposition. 

 We owe our first information regarding this decomposition to Theodor Hartig. 4 

 This author found an important nitrogenous substance in seedlings, which he 

 designated by the name "Gleis." It developed later that Hartig's "Gleis" is 

 identical with asparagin. Boussingault 5 asserted that asparagin appears in all 



1 Korsakoff, Marie, Ueber die Wirkung des Natriumselenits auf die Ausscheidung der Kohlensäure 

 lebender und abgetöteter Hefe. Ber. Deutsch. Bot. Ges. 28: 334-338. iqio. 



- Bayliss, W. M. and Starling, E. H., Die chemische Koordination der Funktionen des Körpers. Ergeb. 

 Physiol. 5: 664-697. 1906. 



3 Lusk, Graham, The elements of the science of nutrition. 2nd ed. 402 p. London and Philadelphia, 

 1909. 



4 Hartig, Theodor, Entwickelungsgeschichte des Pflanzenkeims, dessen Stoffbildung und Stoffwandlung 

 während der Vorgänge des Reifens und des Keimens. Leipzig, 1858. 



5 Boussingault, 1860-1861. [See note 5, p. 2.] Vol. 4, p. 265. 



' Of course this is a figurative way of describing these phenomena. The "necessity" for an 

 enzyme, or the need of the work it can do is not a reason for its being produced. — Ed. 



m This section is numbered §6 in the German. The numbering of the 7th Russian edition is 

 here followed. — Ed. 



