STUDIES ON FERMENTATIOX. 181 



it is difficult to eliminate two sources of error. On the one 

 hand, it is beyond doubt that cells of ferment are actually 

 scattered over everything, and that, consequently, they may 

 easily get into the experimental liquid along with the spores 

 that we sow, and so occasion mistakes.* On the other hand, 

 there are a great many fungi which develop budding pro- 

 cesses similar to yeast, but incapable of producing fermen- 

 tation, which yet in some cases spring directly from spores 

 as well as from mycelium, especially -we may instance exo- 

 ascus. This last observation is especially applicable to the 

 extraordinarily numerous variety of fungi which rank under 

 the Dematiei and Sphaeriacei, and which I shall term, for 

 convenience of naming, dematium pullulatn. 



We shall conclude this paragraph with a remark that has 

 doubtless presented itself to the minds of our readers, which 

 is, that it would be impossible to carry out the experiments 

 we have described if we could not make sure of dealing: with 

 pure ferments, or, at least, with mixtures the components 

 of which are sufficiently well known for us to assign to each 

 the effect produced by it in the total phenomena observed. 

 It would be extremely difficult to continue growths of yeast- 

 deposit in sweetened water or in a moist atmosphere if the 

 little plant were mixed with spores of other fungoid growths, 

 a variety of ferment-forms, and germs of bacteria, vibrios, or 



* The gei-ms of ferments are less widely diffused thau M. de Bary sup- 

 poses, as may be seen from our observations in Chap. III. See, too, our 

 Memoir of 1862, 8ur Its Oenerations dites Spontanees, p. 49. It is only iu a 

 laboratory devoted to researches on fermentation, or places such as vaults, 

 cellars, and breweries, that the air holds appreciably in suspension cells of 

 ferments, ready to germinate in saccharine media. If we except these 

 particular circumstances, ferment is not very largely diffused, save on the 

 surface of fruits and the wood of the trees which bear them, and perhaps, 

 also, on some other plants. The particles of dust held in suspension in 

 any atmosphere whatever rarely produce fermentation in pure must 

 even when we take all possible precautions, so that the action be not 

 overlooked ; for true fermentation may be hidden by fungoid growths, 

 when there is much air and but a small quantity of saccharine liquid 

 present. 



