482 BOARD OF AGRICULTUBE. 



great expense in cellars. It is easier to prove that he did this by a French- 

 man than by a German. 



These investigations into fermentation put us in possession of the 

 inestimable fact that each fermentation is caused by its own kind or 

 kinds of micro-organisms. These different germs living in the same 

 medium consume its constituents in different proportions. They leave in 

 it as the result of their life-processes different substances. Some of these 

 are well-flavored and some are not; some are poisons and cause disease; 

 others are foods that we need. The dairy, as we have it today, depends 

 on this fact. Bad butter means that the wrong germs have found their 

 way into it or the cream from which it was made. The different flavors 

 of samples of butter depend on the kinds of bacteria that produce them. 



FORMS, HABITAT, ETC., OF BACTERIA. 



Figui-e I, taken from the scrapings of teeth that had been strangers 

 for some days to the tooth brush, shows the different forms which the 

 bacteria assume. Sometimes they are long rods (1); sometimes they are 

 short rods (4); again, they are bent rods (3); still others are little spheres 

 (5), and others yet are long spiral lines (2). 



They are to be found in surface water in all inhabited places. Deep 

 well water never has them, and spring water generally does not. 



They vary in number in water from few or none up to many millions 

 per cubic inch. 



They are present in the air generally, but not everywhere. On high 

 mountains there are none. In a M-^ell-regulated hospital, several thou- 

 sands are to be found in every cubic yard of air. They are fewer in open 

 parks of cities, and fewer still in the country. 



There are none in milk, if it is drawn with every scientific precaution; 

 this is, however, never done in practice. If milk is drawn in a dusty, 

 carelessly kept stable, in a wide-mouthed bucket, they are always very 

 numerous in it. Milk on the market in Halle has been found to contain 

 750,000,000 to the cubic inch. 



They are numerous in the soil wherever there is loam; pure clay or 

 sand is without them. They are not found deep in the ground under nor- 

 mal conditions. 



SIZE OF BACTERIA. 



It follows from the figures given above that bacteria are very small; 

 the smallest are less than one two-hundred-and-fifty-thousandth of an 

 inch. The bacillus tuberculosis (Fig. II) is so small that 125,000 can lie 

 side by side in the space of an inch. 



Their rapid multiplication under favorable conditions enables them to 

 do the great harm or good which they do. Bacteria multiply by sim- 

 ple fission; they divide so rapidly that one can become the ancestor of 



