424 YEAST 



they would be preserved for any time. He tried these experi- 

 ments, particularly with the must of wine and with the wort 

 of beer ; and he found that if the wort of beer had been 

 carefully boiled and was stopped in such a way that the air 

 could not get at it, it would never ferment. What was the 

 reason of this ? That, again, became the subject of a long 

 string of experiments, with this ultimate result, that if you 

 take precautions to prevent any solid matters from getting 

 into the must of wine or the wort of beer, under these cir- 

 cumstances that is to say, if the fluid has been boiled and 

 placed in a bottle, and if you stuff the neck of the bottle 

 full of cotton wool, which allows the air to go through, and 

 stops anything of a solid character however fine, then you 

 may let it be for ten years and it will not ferment. But if 

 you take that plug out and give the air free access, then, 

 sooner or later fermentation will set up. And there is no 

 doubt whatever that fermentation is excited only by the 

 presence of some torula or other, and that that torula pro- 

 ceeds in our present experience, from pre-existing torulse. 

 These little bodies are excessively light. You can easily 

 imagine what must be the weight of little particles, but 

 slightly heavier than water, and not more than the two- 

 thousandth or perhaps seven-thousandth of an inch in 

 diameter. They are capable of floating about and dancing 

 like motes in the sunbeam ; they are carried about by all 

 sorts of currents of ah* ; the great majority of them perish ; 

 but one or two, which may chance to enter into a sugary 

 solution, immediately enter into active life, find there the 

 conditions of their nourishment, increase and multiply, and 

 may give rise to any quantity whatever of this substance 

 yeast. And, whatever may be true or not be true about 

 this " spontaneous generation," as it is called, in regard 

 to all other kinds of living things, it is perfectly certain, 

 as regards yeast, that it always owes its origin to this process 

 of transportation or inoculation, if you like so to call it, from 

 some other living yeast organism ; and so far as yeast is 

 concerned, the doctrine of spontaneous generation is abso- 

 lutely out of court. And not only so, but the yeast must 

 be alive in order to exert these peculiar properties. If it be 

 crushed, if it be heated so far that its life is destroyed, that 

 peculiar power of fermentation is not excited. Thus we 

 have come to this conclusion, as the result of our inquiry, 

 that the fermentation of sugar, the splitting of the sugar 

 Into alcohol and carbonic acid, glycerine, and succinic acid, 



