Fermentation and Kindred Phenomena. 77 



elements by the disturbance of equilibrium is also communicated 

 to the elements of the bodies which come into contact with 

 them. 



Then athird view was advocated by Berzelius and Mitscherlich, 

 viz., that the yeast acts, as the chemist phrases it, " catalytically," 

 that is to say, causes the decomposition of the sugar by its 

 presence while it remains unchanged. This explanation is the 

 more plausible as many such actions are known. For instance, 

 the decomposition of bleaching powder into chloride of cal- 

 cium and oxygen by peroxide of cobalt. 



I do not wish to detain you longer with these historical 

 particulars, nor can I follow out the chain of arguments which 

 eventually led to the correct explanation of fermentation. It 

 must be sufficient for me to state that Pasteur proved conclusively 

 that the fermentation of sugar is inseparably connected with 

 the life of the yeast cell ; in fact, that the sugar is the soil or 

 food upon which the yeast lives, and that the carbonic acid and 

 spirit are waste products— just as the carbonic acid which is 

 exhaled from our lungs is a waste product, the carbon being 

 derived from the food we eat. 



A few words as to the structure and life history of the 

 yeast cell. When yeast is examined with the microscope 

 under a rather high power it is found to consist of myriads 

 of minute globules, which are round or oval. Careful investi- 

 gation has shown that these globules or "cells" consist of 

 a mass of protoplasm surrounded by cellulose. They are, in 

 fact, paper bags full of protoplasm. The protoplasm, like 

 the cellulose envelope, is colourless, sometimes homogeneous, 

 sometimes composed of small granulations. In the protoplasm 

 are usually seen one or two dots or " vacuoles," as they are 

 called, which are cavities containing liquid. If the growing 

 yeast cells are carefully watched under the microscope they are 

 seen to alter their appearance with considerable rapidity. 

 Sometimes at one, sometimes at two ends, small bladder-like 

 prominences make their appearance, which gradually enlarge, 

 and at last having attained a considerable size lessen in diameter 

 at their base, and eventually separate themselves from the parent 

 cell and lead an independent existence. 



