THE HISTORY OF BACTERIOLOGY. 67 



nutrition of the growing yeast, but that otherwise it did 

 not exert any influence in transforming the sugar into lactic 

 acid, as had hitherto been maintained by Liebig. 



Some idea of the delicacy of Pasteur's experiments may be gathered 

 from his observations on the conversion of racemic or paratartaric acid by 

 a living ferment into right-tartaric acid (which in turn was capable of 

 undergoing further fermentation) and into left-tartaric acid, which remained 

 unaltered. He had already noted that the material in which fermentative 

 changes took place, determined, in a very marked degree, the nature of the 

 fermentation process. For instance, on adding dust, which of course con- 

 tained a considerable number of different organisms, to sterilized urine, an 

 ammoniacal or putrefactive fermentation took place ; whilst on adding the 

 same dust to sterilized milk an acid fermentation, as evidenced by the 

 curdling of the milk, ensued, whilst in each case there seemed to be a 

 special development of one particular organism. He had of course to 

 contend with the difficulties involved in obtaining isolated organisms or 

 pure cultivations, and for this reason he was for some time heavily handi- 

 capped. 



All the forms of ferment-producing organisms which 

 Pasteur had studied up to this point he spoke of as 

 vegetable or yeast forms, and it was long before he was 

 able to induce butyric acid fermentation. He at length 

 found, however, a form which he distinguished as an 

 infusiorian, in contradistinction to the vegetable or yeast 

 form. This he describes as occurring in the form of small, 

 straight, cylindrical rods, somewhat rounded at the ends, 

 occurring either singly or in jointed chains of three, four, 

 or more, about 2/j broad and from two to ten times as 

 long as broad. The organism has a slight gliding motion, 

 and its reproduction takes place apparently by vegetative 

 growth and transverse division. The physiological or bio- 

 logical peculiarity of this organism is that it can exist 

 apparently without a trace of organic nitrogen ; whilst, like 

 the vegetable ferments with which Pasteur had been working, 

 it can also live without oxygen, and although in form it is 

 like a vibrio, it differs from the vibrios in this respect and 

 also in that it is able to bring about fermentation. 



In 1863 he found a second anaerobic "vibrio," which he 

 succeeded in cultivating. He prepared a solution contain- 

 ing tartarate of lime, ammonia, potassium, and yeast ash, 

 rendered it sterile or germ-free by boiling, and covered it 

 with a thick layer of oil. To the fluid thus prepared he 

 added a minute quantity of the organic deposit resulting 

 from spontaneous fermentation of tartarate of lime ; the 



