234 SCIENCE PROGRESS. 



Pasteur made his first experiments on fermentation with 

 milk, in which he recognised, as the process of fermentation 

 went on, the lactic ferment, which he described as little 

 rods with slightly constricted centres, so small that their 

 diameter was scarcely the twenty-five thousandth of an inch. 

 This rod multiplied by a process of division, each one into 

 two shorter rods which, in turn, assumed the shape and size 

 of the original. To isolate this organism and to obtain a 

 comparatively pure culture, Pasteur boiled a little yeast 

 with from fifteen to twenty times its weight of water ; he 

 then carefully filtered the liquid, dissolved in it about 

 5 per cent, of sugar, and then added some chalk. This 

 he seeded with a trace of the ordinary lactic fermentation 

 deposit, with the result that the next day a lactic acid 

 fermentation had set in, the liquid became turbid, the 

 chalk disappeared, and a deposit of lactic ferment 

 gradually took its place. He then repeated his previ- 

 ous experiment of adding this special ferment to small 

 quantities of crystallisable salt of ammonia and phos- 

 phates of potash and magnesia. In this he found also, 

 that although there was no organic matter present beyond 

 that which he had introduced in the shape of his organ- 

 isms, they still continued to multiply and to give rise to the 

 typical fermentation, both yeast and the lactic ferment act- 

 ing in the same way, each giving rise to its own special pro- 

 duct. By these experiments both Liebig's and Berzelius's 

 theories were at once shattered, as the carbon was supplied 

 by the fermentable substance, whilst the process of fer- 

 mentation could not be due to the action of oxygen on 

 nitrogenous substances, as nitrogenous matter did not enter 

 into the constituents of the solution, and still a vigorous 

 fermentation had taken place. Pasteur concluded that 

 fermentation was simply a phenomenon of nutrition — the 

 nutrient substance beinQf the suQ-ar, the organism nourished 

 being the ferment germs, — whether they were lactic acid 

 organisms or yeast — the organisms contriving to obtain the 

 materials necessary for the building up of their complex 

 organisation from the sugar and the purely mineral elements. 

 Then followed the discovery of the butyric ferment, 



