220 THE ORGANISMS IN YEAST. 



" Etudes sur la Biere," says of this : — " Experiment has proved 

 that an ebullition of some minutes gives, to a malt infusion spe- 

 cially, an absolute freedom from change when in contact with pure 

 air — that is to say, with air deprived of the organic germs which 

 it invariably contains,"* and as such infusions are among the best 

 media for the culture of industrial ferments, and as any doubt as to 

 the ready practical sterilisation of the nutrient fluids employed 

 would render the results obtained worthless, I have thought it well 

 to refer to some special examples. Some weeks since, a friend 

 prepared for me a series of flasks, containing malt infusions, and 

 as he was unaware of the object for which the preparations were 

 made, and simply acted on my instructions conveyed through a 

 third party, no preconceived ideas of mine could in any way have 

 affected the result. The infusion was made from a good sample of 

 malt in distilled water at about i8o° F., and was filtered hot into 

 the flasks, which, after the closing of the necks with cotton wool, 

 were briskly boiled, each for some ten minutes. They were then 

 placed on a shelf, where they remained for a considerable time, 

 and, with the exception of an albumenoid precipitate, which 

 formed on cooling, the contents have remained unaltered, and 

 without the slightest indication of the presence of ferment-life. It 

 may be useful to point out that the same thing has been shown to 

 be true of milk, and of the liquid known as '' Pasteur's cultivating 

 fluid," by Professor Lister, who has given the name of Bacterium 

 lactis to the organism to which the acid change in the former is 

 due — and others ; while Dr. W. Roberts, in his address before the 

 British Medical Association at Manchester in the year 1877, exhi- 

 bited a great number of organic infusions and secretions which had 

 been rendered permanently sterile by the application of proper 

 means for the destruction or removal of organised cell-life. We 

 may, therefore, be satisfied that cultivating liquids may be readily 

 freed from the germs of organised life, and also that, practically 

 speaking at any rate, no confusion or error is to be apprehended in 

 our cultures from any spontaneous evolution of organised cells. 



The next step is to ascertain what media are best adapted to 

 the culture of the special class of organisms which it is desired to 

 investigate. And that such is not an immaterial point is shown by 



* Etudes sur la Bierre, chap. III., p. 33. 



