"^18 



THE ORGANISMS IN YEAST. 



freed. At first, it was thought that a brisk boihng of the cultivat- 

 ing liquid for a short time would effectually destroy any organic 

 life that might be present, seeing that protoplasm is coagulated at 

 a temperature far below the boiling-point of water, and that by 

 sealing up the flask while ebullition was still in progress, the liquid 

 within would be protected from aerial contamination ; and there 

 can be no doubt that, within certain limits^ both these propositions 

 are perfectly correct. But it is evident that the sealing-up of the 

 flasks in this manner at a temperature of ebullition, however 

 appropriate for elucidating the beginnings of life, is inconsistent 

 with the cultivation of cell-life in the manner we require, and 

 another difficulty arises in the fact that the efficacy of a few 

 moments' boiling for the destruction of such organisms as may be 

 present, is by no means certain, unless the absence of certain 

 special forms be first assured. 



The first point — that of excluding aerial germs from a liquid 

 which had been — in whatever manner — rendered sterile^ under 

 conditions which at the same time admit of the practical culture 

 and study of any desired organism, was met by the employment of 

 Pasteur's cultivating flasks, having a long, narrow, curved neck, 

 which is plugged with cotton wool, and a shorter side-neck, with 

 India-rubber collar, capable of being closed with a glass plug. 

 The liquid being boiled in such a flask, the escaping steam des- 

 troys in its passage any germs of life which may exist, either on 

 the interior surfaces of the flask, or in the cotton wool through 

 which it makes its exit, and when, on the flask cooling, the air 

 re-enters, the latter serves as an effectual filter for the stopping of 

 any particles which would otherwise be introduced, whether living 

 germs or otherwise. If we presume for a moment that this boiling 

 is sufficient for the destruction of organised life, we shall now have 

 a nutrient liquid free from the agents of change, and surrounded 

 by an equally pure atmosphere, into which the organism to be 

 cultivated is introduced or "sown" by dropping in a bit of plati- 

 num wire, or foil, which, after being heated to redness, is touched 

 with the organism to be cultivated, so that a little adheres, and is 

 admitted to the flask by the momentary removal of the stopper in 

 the short neck. If the manipulation be conducted with ordinary 

 dexterity and speed, no harm is likely to arise from the short 



