each cell forming two bacteria, which in turn divide 

 again, forming four, etc. 



Some species of bacteria, which reproduce under or- 

 dinary circumstances by cell-division, are capable of form- 

 ing spores, if their life is imperiled by unfavorable con- 

 ditions. These spores form in the mothercell and the 

 very resistant to outside influences like heat and cold. 

 When coming under favorable conditions again the spores 

 begin to grow and the reproduction goes on in the 'usual 

 way by cell-division. 



Bacteria of the spore-forming species are a great 

 danger to the quality of milk-products. The spores can 

 be killed only by heating to temperatures by which the 

 nature of the milk or the products is altered and thus 

 lowered. 



Some species are useful in the manufacturing-pro- 

 cesses of various articles of human food, i. e. butter, 

 cheese, etc., or by promoting the growth of useful plants 

 like clovers, vetches, peas and beans, while others may 

 cause troubles by producing compounds that are undesir- 

 able (racidity in butter, bitter taste in milk,) or plant dis- 

 eases. 



All the dangerous contagious diseases in man and 

 animals are caused by bacteria. 



The undesirable kinds are most often found in filth 

 and manure, on dusty and rotting feedstuff S, bedding ma- 

 terial, etc. ; hence the great danger connected with feed- 

 ing, manuring of stables, and bedding during milking* 

 time. By these actions the bacteria, adhering to dust- 

 particles are stirred up in the air and fall in the shape 

 of an invisible rain in the milk-pail. 



The rapidity of bacterial growth depends upon the 

 character of the medium in which they live and upon the 

 temperature thereof. The more water a medium contains 

 the more rapid is, in general, their growth. 



Each species of bacteria is limited in its reproduction 

 to certain temperatures, above and below which it ceases ; 



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