FERMENTATION. 133 



In the lactic acid fermentation it does not appear to be 

 necessary that any process of hydration should take place, 

 as there is here merely an exact division of one molecule of 

 sugar into two molecules of lactic acid, there being neither 

 addition nor loss of either oxygen or hydrogen. It must, 

 however, be borne in mind that the lactic acid fermentation 

 is frequently accompanied by the formation of CO 2 , in which 

 case, of course, the process is not nearly so simple. 



By fermenting lager beer at from 30 to 34 C., Chr. Hansen found that 

 there was developed a form of bacterium made up of long chains, of dumb- 

 bell or hour-glass shaped organisms, of bacteria as long curved or straight 

 threads ; whilst at irregular intervals were formed spindle-shaped or club- 

 shaped bacteria, even when the nutrient conditions still continue good at a 

 late stage of the growth. That these organisms, however, were not all 

 alike, Ilansen proved by the fact that some of them are stained yellow by 

 iodine, whilst with others a blue reaction was obtained. The conditions 

 necessary for the development of this organism, and the production of acetic 

 acid, are a high temperature from 30 to 34 C. and a plentiful supply 

 of oxygen. So necessary is this latter that a film forming on the surface 

 is all that there is to denote the presence of an organism, the fluid 

 beneath, from which free oxygen is cut off, remaining perfectly clear ; and 

 Hansen even gives this as a diagnostic feature to enable an observer to 

 determine whether he is dealing with pure cultivations of these mycodermi 

 or not, as, wherever other bacteria are present, roughly speaking, turbidity 

 is set up. 



It is a curious fact that the pure lactic fermentation cannot 

 go on when the medium is too acid, and it is only by remov- 

 ing the lactic acid as it is formed that a complete trans- 

 formation even of milk sugar into lactic acid can be obtained. 

 This fact was observed long before the exact nature of the 

 process was understood ; and in all the earlier methods 

 devised for the preparation of this substance the daily 

 neutralization of the fluid with chalk or carbonate of soda 

 played a most important part. That the process is essen- 

 tially the same as the others, in so far as it is the result 

 of the activity of micro-organisms, was proved by Pasteur, 

 who found that by sowing the lactic acid ferment, which 

 he described as composed of small globules or short 

 joints, either isolated or in mass, in a fluid which he 

 had found specially suitable for alcoholic fermentation, 

 active lactic fermentation was coincidentally set up, and 

 lactic acid was found present along with the resulting 

 alcohol ; whilst, as we already know, if no lactic acid fer- 

 ment be introduced, either accidentally or intentionally, no 



