185 



have developed parasitic properties ; this being brought about through a course 

 of adaptation, which has enabled them to exist under the changed conditions. 

 There ai-e other bacteria possessing pathogenic properties which can be treated in 

 such a manner as to cause them to lose their virulency, among these a notable one 

 being anthrax, which when carried through a course of gelatine cultures is no 

 longer pathogenic. The pathogenic properties may be restored, however, by ap- 

 propriate treatment, such as cultivation at the body temperature in specially pre- 

 pared media. Of course, the conditions for a saprophytic mode of life are more 

 generally met with than those for the development of parasitic life, so that it is 

 presumable that most organisms become adapted to them. 



About twenty years ago yeast was used in water to spray plants in green- 

 houses for the purpose of getting rid of insect pests.* This treatment was based 

 upon the belief that the yeast entered the body of the insect and produced a 

 growth which was fatal. As pure yeast was nut used, and as yeasts usually have 

 associated with them bacteria and molds, the use of yeast for such purposes is not 

 conclusive in proving it to be pathogenic. 



Somewhat later a yeast, S. Allii, was grown on the bulbs of onions, and caused 

 them to rot by reducing them to a gelatinous condition, t during which time a 

 powerful odor was emitted by them. Bacteria were also found in conjunction 

 with the yeast in the onions. 



In recent years, since accurate methods have been devised for the separation 

 of the various species and varieties of yeasts, a more definite knowledge has been 

 obtained of their properties. It has been determined that while most of them 

 possess the property of exciting alcoholic fermentation, that, aside from this, they 

 differ widely in the formation of other products that accompany the fermentation. 

 For example, two species that were found on the fruit of Ilex aquifolium, though 

 having the same habitat, gave different products, the one {S. ilicis Gronlund) 

 gave a disagreeable, bitter taste to wort, while the .other (S. a(/«i/bZu" Gronlund) 

 gave a disagreeable, sweet taete. Of two ellipsoid species studied by Will, the 

 one gave a rough, bitter after-taste, while the other imparted a disagreeable, aro- 

 matic taste during the fermentation, and a bitter, astringent after-taste to wort. 

 Then of two species studied by Hansen, one {S. Pastorianut I.) gave a disagree- 

 able, bitter taste and unpleasant odor to wort, while the other {S. anomalom) gave 

 an ethereal, fruity odor. One might go on at length giving examples of the dif- 

 ferences in the products of yeasts, but from what has been given, it can be seen 

 that the products differ widely, and that it is highly probable that some of these 



•Hagen. H. A., " Nature," Vol. XXI, p. 611. 1880, April. 

 tSorokin, N., Jour. Roy. Mier. See, 1889, Pt. I. 



