INTRODUCTION. 1 1 



unsoundness of beer, but as they are readily killed at a 

 temperature of 60 C., they may easily be got rid of. 



In the process of baking, as carried on in this country, 

 there is a regular conversion of some of the starch of the 

 flour into sugar by the yeast used this sugar being in 

 turn converted into alcohol and carbonic acid gas, to 

 the setting free of which the " rising " of bread is due. 

 The baking that follows serves three purposes ; it kills 

 the ferment, it fixes the remaining starchy matter in posi- 

 tion, and it drives off the alcohol and the carbonic acid. In 

 the baking of other kinds of bread certain other organisms 

 are said to play a part ; for instance, the Saccharomyces 

 minor (Engel) was supposed to be the active fermenting 

 agent in the manufacture of rye bread, but more recently 

 this organism has been superseded, and the work of fermen- 

 tation has been assigned to a bacillus Bacillus Panificans 

 (Laurent) which in pure cultivations was found to be capable 

 of setting up all the characteristic fermentation changes in the 

 dough of black bread. This organism is made up of short 

 motile rods, from which threads may be formed, these threads 

 (in which spores are sometimes found) interlacing to form a 

 film, especially when it is grown on the surface of nutrient 

 liquids. Its spores are almost as resistant as those of the 

 hay bacillus, and can only be killed by being subjected to 

 boiling heat for a period of at least ten minutes. 



Jorgensen, summing up Laurent's investigation, says : 

 " The bacillus usually dissolves the gluten substance of the 

 dough, grows in starch paste, and in mixtures of saccharose 

 and mineral substances. It is found in an active state in 

 large quantities in bread, and according to the author's 

 researches, it can withstand for twenty hours the action of 

 an artificial gastric juice. In the excreta it is found still 

 more abundantly, and it appears to be generally distributed 

 in plants and in various substances." More recent researches, 

 however, have thrown some discredit even on the Bacillus 

 Panificans ; Diinnenberger maintaining that these bacteria 

 are merely an impurity, and that in all cases the fermenta- 

 tion of bread is due to an alcoholic-forming organism a 

 saccharomyces in all cases proving the best agent for bring- 

 ing about this fermentation. 



Certain forms of unsoundness of bread are also due to 

 micro-organisms. In addition to bleeding-bread (caused by 



