' 238 STUDIES ox FERMENTATION. 



proportion varies in a precise manner, according to conditions 

 which we shall have occasion to specify, it is also greatly out 

 of proportion to the weight of the yeast. We repeat, the life 

 of no other being, under its normal physiological conditions, 

 can show anything similar. The alcoholic ferments, therefore, 

 present themselves to us as plants which possess at least two 

 singular properties : they can live without air, that is, without 

 oxygen, and they can cause decomposition to an amount which, 

 though variable, yet, as estimated by weight of product formed, 

 is out of all proportion to the weight of their own substance. 

 These are facts of so great importance, and so intimately 

 connected with the theory of fermentation, that it is indis- 

 pensable to endeavour to establish them experimentally, with 

 all the exactness of which they will admit. 



The question before us is whether yeast is in reality an anaero- 

 bian plant, and what quantities of sugar it may cause to ferment, 

 under the various conditions under which we cause it to act. 



The following experiments were undertaken to solve this double 

 problem : — We took a double-necked flask, of three litres (five 

 pints) capacity, one of the tubes being curved and forming an 

 escape for the gas ; the other one, on the right hand side 

 (Fig. 59), being furnished with a glass tap. We filled this 

 flask with pure yeast-water, sweetened with 5 per cent, of 

 sugar candy, the flask being so full that there was not the least 

 trace of air remaining above the tap or in the escape tube ; this 

 artificial wort had, however, been itself aerated. The curved 

 tube was plunged in a porcelain vessel full of mercury, resting 

 on a firm support. In the small cylindrical funnel above the 

 tap, the capacity of which was from 10 c.c. to 15 c.c. (about 

 half a fluid ounce) we caused to ferment, at a temperature of 

 20° or 25° C. (about 75° F.), five or six cubic centimetres of the 

 saccharine liquid, by means of a trace of yeast, which mul- 

 tiplied rapidly, causing fermentation, and forming a slight 

 deposit of yeast at the bottom of the funnel above the tap. We 

 then opened the tap, and some of the liquid in the funnel 

 entered the flask, carrying with it the small deposit of yeast. 



