CHAPTER XLIV. 



FERMENTATIOX BY MUCORS. 



§ 238.— IntPamolecular Respiration and Alcoholic 



Fermentation. 



The exhalation of carbon dioxide, to which the name respiration 

 has been given, may occur, in both animal and vegetable cells, 

 under two widely different sets of conditions : either in the 

 presence and unrestricted access of oxygen, or in the entire 

 absence of this gas. In the former case the process is termed 

 oxygen respii-ation ; but only a few remarks can here be made 

 in connection therewith, for the most part to supplement the 

 thorough description given in Pfeffer's (III.) Handhool; of Verje- 

 tahJe PhydrAogij. The volumetric ratio between the absorbed 

 oxygen and the evolved carbon dioxide, or, as it is termed, the 

 quotient of respiration (CO., : O.,), was found by Saussure, as long 

 ago as 1833, to vary with the nature and actual condition of the 

 plant under examination, as well as with the conditions of 

 nutrition. With regard to this latter factor, it was shown by 

 DiAKOxow (II.), in the case of Penicillium ijlaucum, that — other 

 conditions being equal — the quotient of respiration is equal to 

 unity when the food.stuff is sugar, but 2.9 when tartaric acid 

 forms the nutrient substance. Puriewitsch (III.) then demon- 

 strated, in the case of Aspi'ir/iUus niger, that an increase in the 

 concentration of the nutrient solution causes the quotient to rise 

 at first, but afterwards to recede. The influence of temperatui-e 

 on the quotient of respiration was investigated by C. Gerber (I.) 

 in cultures of the last-named fungus grown in Raulin's nutrient 

 solution, with an addition of tartaric (malic or citric) acid, either 

 alone or in conjunction with saccharose, as the organic foodstuff. 

 Mention has already been made in |:^ 233 of the influence of the 

 degree of illumination on the quotient of respiration, as well as 

 on a few other points in connection therewith. 



We shall have to deal in a more thoroughgoing manner with 

 the second kind of respiration, to which the name of intra- 

 molecular respiration has been given in consequence of a pro- 

 posal made by Pflueger in 1875. This phenomenon consists of 

 the persistent exhalation of carbon dioxide by cells excluded 

 from a supply of free oxvgen. The sole materials for this 



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