<j 7 3 THE POPULAR SCIENCE MONTHLY 



time, by simply boiling the wort and closing the vessel in which the 

 boiling fluid is contained, in such a way as thoroughly to exclude air ; 

 and he shows that, if a little yeast be introduced into such wort, after 

 it is cooled, the wort at once begins to ferment, even though every pre- 

 caution be taken to exclude air. And this statement has since received 

 full confirmation from Pasteur. 



On the other hand, Schwann, Schroeder and Dusch, and Pasteur, 

 have amply pi*oved that air may be allowed to have free access to 

 beer-wort, without exciting fermentation, if only efficient precautions 

 are taken to prevent the entry of particles of yeast along with the air. 



Thus, the truth, that the fermentation of a simple solution of sugar 

 in water depends upon the presence of yeast, rests upon an unassaila 

 ble foundation ; and the inquiry into the exact nature of the substance 

 which possesses such a wonderful chemical influence becomes pro- 

 foundly interesting. 



The first step toward the solution of this problem was made 

 two centuries ago by the patient and painstaking Dutch naturalist, 

 Leeuwenhoek, who in the year 1680 wrote thus : 



I have frequently examined the ferment of beer, and always observed 

 globules floating through the pellucid liquor; I also noticed very clearly that 

 each single globule of the ferment gave origin to six other distinct globules, 

 which, in size and form, I found, on careful observation, to correspond to the 

 globules of our blood. But I conceived these globules to be due to and formed 

 from the starchy particles of the wheat, barley, oats, etc., dissolved in and 

 mixed with hot water ; and in this water, which as it cools may be called beer, 

 numerous minute particles joined together, and formed a globule, the sixth part 

 of the compound globule, and thus the globules formed continuously in sixes." 1 



Thus Leeuwenhoek discovered that yeast consists of globules float- 

 ing in a fluid ; but he thought that they were merely the starchy par- 

 ticles of the grain from which the wort was made, rearranged. He 

 discovered the fact that yeast has a definite structure, but not the 

 meaning of the fact. A century and a half elapsed, and the investiga- 

 tion of yeast was recommenced almost simultaneously by Cagniard de 

 la Tour, in France, and by Schwann and Ktitzing, in Germany. The 

 French observer was the first to publish his results ; and the subject 

 received at his hands and at those of his colleague, the botanist Turpin, 

 full and satisfactory investigation. 



The main conclusions at which they arrived are these : The globu- 

 lar, or oval, corpuscles which float so thickly in the yeast as to make it 

 muddy, though the largest are not more than ^oVo" f an U1CU m diam- 

 eter, and the smallest may measure less than - , ^ of an inch, are liv- 

 ing organisms. They multiply with great rapidity, by giving off 

 minute buds, which soon attain the size of their parent, and then 

 either become detached or remain united, forming the compound glob- 



1 Leeuwenhoek, "Arcana Naturae Detecta." Ed. Nov., 1721. 



