MEANS OF SEPARATING ROTARY SUBSTANCES 45 



as the result of the development of one of those organisms 

 which invade infusions, and then a drop of this clouded 

 liquid sufficed to induce a fermentation in a new flask. 



Thus far nothing surprising: we have before our eyes 

 one of those phenomena of decomposition of organic 

 matter which are constantly taking place around us. 

 But here is where the investigator awakes and the origi- 

 nality begins. For others the fact was commonplace; for 

 Pasteur it was life engaged in a struggle with a compound 

 endowed with rotary power. This form of plant life 

 which grew and developed in the flask was composed of 

 cells giving birth to dissymmetrical products, as do all 

 living cells, and then there presented itself quite natur- 

 ally and imperatively the following question: how will 

 this organism behave in a solution of paratartrate? 



Let us transfer a drop of the fermented liquid of right 

 tartrate of ammonia to a solution of paratartrate of 

 ammonia. Things follow their course, and nothing out- 

 wardly distinguishes these two fermentations. But let 

 us study them with a polarization apparatus. Let us 

 filter, at definite intervals, a portion of the solution of 

 paratartrate and pass through it a ray of polarized 

 light, and we shall see that this liquid, inactive in the 

 beginning, has acquired a left rotary power which in- 

 creases little by little till it reaches a maximum. At 

 this moment fermentation is suspended, the liquid clears, 

 it contains no longer any of the right-handed salt which 

 is the only one the fermentation has attacked and trans- 

 formed. The left-handed salt has been respected and 

 can be recovered by evaporation. 



The phenomena, it is true, do not always proceed 

 in just this manner. Everything depends on the micro- 

 scopic organism which is sown, and developed, in the 

 liquid. Pasteur has never described the one which he 

 observed; it would seem that he had been working with a 



