l886.] NEW-YORK MICROSCOPICAL SOCIETY. 43 



bouillon, and the contents are then carefully poured upon a 

 strip of glass, or upon a flattish watch-crystal that has been 

 sterilized at a high temperature. At the end of the second day, 

 or beginning of the third, there will appear upon the layer of 

 gelatine some whitish spots, which, when examined under the 

 microscope, will be found to be bacilli. Each rod has produced 

 offshoots, and its progeny occupies a particular space that 

 forms what is called a " colony." Every colony of the same 

 species has an aspect that is peculiar to it, and, if several 

 species be found in flour, we shall see several sorts of colonies. 

 But there is one form of colony that predominates in a truly 

 astonishing proportion. By its perfectly circular form, by its 

 color, and by its mode of development in cultures upon gela- 

 tine, it may be recognized in a mixture of the bacteria of putre- 

 faction. The rods of this species are found in bread after it 

 has been baked, and more than 500,000 of them have been 

 seen in a gramme of leavened bread — say 250,000,000 to the 

 pound. These figures may cause those to shudder who have a 

 horror of microbes ; yet these bacilli are not only harmless, but 

 are even powerful aids to us in the digestion of food. 



Let us examine their mode of life in dough. We already 

 know that, under the action of water and soluble ferments, 

 there is an increase of the peptones and sugars in the dough. 

 The germs of the Bacillus disseminated in flour soon multiply 

 upon contact with water and soluble aliments. This species, 

 moreover, has the property of depriving dough of a portion of 

 its gluten, and of reducing the latter to soluble substances. In re- 

 turn, it improves the quality of bread. It lives and breathes, and 

 consequently produces carbonic acid, which forms cavities in 

 consequence of the elasticity of the gluten. It is due to this 

 action that bread is rendered lighter and more agreeable to eat. 

 Aside from this important function, the bread-bacillus brings 

 about quite complicated actions in the dough. It will suffice to 

 mention the production of acetic, butyric and lactic acids, 

 which give bread a very pronounced acidity. There is no 

 longer any possible doubt of it — the bacillus under considera- 

 tion is the bacterium of panary fermentation, and so the name 

 Bacillus panificans has been proposed for it. 



And now as to the physiology of the organism : It is easily 

 cultivated ii) Koch's nutritive gelatine, acid or slightly alka- 



