206 



PHYSIOLOGY OF NUTRITION 



ture in beer-wort is transferred to gelatine and the cells multiply and develop 

 into giant colonies upon the gelatine surface. The form of colony is always con- 

 stant for the same species and different forms of colonies are produced by 

 different kinds of yeast. The drawings of Fig. 90 show how distinct are the 

 giant colonies of various different yeasts. 



It has been seen that alcoholic fermentation is a process involving the action 

 of enzymes e (see page 204). Besides carbohydrates, such ketonic acids as pyro- 

 tartaric acid may also be decomposed in this way, as was shown by Neuberg 1 

 and his co-workers. Pyrotartaric acid is split into carbon dioxide and acetic 



S. pastorianus I. S. pastorianus II. 



S. pastorianus III. 



S. ellipsoideus I. 



Fig. 90.- 



5. ellipsoideus II. Bottom-Fermentation Yeasts. 



-Giant colonies of different yeasts. {After P. Lindner.) 



aldehyde, by a special enzyme, carboxylase, the reaction being represented by 

 the following equation : 



Pyrotartaric acid 

 CH3COCOOH 



Carbon 



dioxide Acetic aldehyde 



= C0 2 + CH3COH. 



The acetic aldehyde thus formed is reduced to ethyl alcohol. Kostychev 2 re- 

 ports that pyrotartaric acid is apparently one of the intermediate products in the 

 breaking down of glucose. Zaliesskii 3 found the enzyme carboxylase in higher 

 plants. 



Reductase is plentiful in yeast, and this enzyme has been shown to play an 



1 Neuberg, C, and Karczag, L., Ueber zuckerfreie Hefegarungen. IV. Carboxylase, ein neues Enzym 

 der Hefe. Biochem. Zeitsch. 36: 68-75. 1911. Idem, same title. V. Zur Kenntnis der Carboxylase 

 Ibid. 36: 76-81. 191 1. Neuberg, Carl, and Kerb, J., Entsteht bei Zuckerfreien Hefegarungen .lEthyl- 

 alkohol? Zeitsch. Garungsphysiol. 1: 114— 120. 1912. 



2 Kostytchew, S., Ueber Alkoholgarung. (I Mitteilung.) Ueber die Bildung von Acetaldehyd bei der 

 alkoholischen Zuckergarung. Zeitsch. physiol. Chem. 79: 130-145. 1912. Kostyschew, S., and Hub- 

 benet, E. (II Mitteilung.) Ueber Bildung von Aethylalkohol aus Acetaldyhyd durch lebende und getotete 

 Hefe. Ibid. 79: 359-374- 1912. 



a Zaleski, W., Ueber die Verbreitung der Carboxylase in den Pflanzen. Ber. Deutsch. Bot. Ges. 31 : 

 349-353- 1913- 



e This and the next following paragraph are not in the German edition and are 

 translated from the 7th Russian edition. — Ed. 



