PREFACE. 



SUCCESSFUL dairying at the present time depends, to a 

 very large extent, upon skill in handling bacteria. It is im- 

 possible to meet the present conditions of the city milk supply, 

 of butter-making and cheese manufacture, without a knowl- 

 edge of the relation of these microscopic organisms. Bac- 

 teriology has become, therefore, a necessary part of dairy 

 courses. The subject is, however, equally important in other 

 directions. The demonstrated connection between milk bac- 

 teria and the distribution of certain diseases has brought the 

 subject of bacteria of milk products forcibly to the attention 

 of boards of health and sanitarians. To meet the needs of 

 such persons and all others interested in the handling of milk 

 is the purpose of this work. . 



Most of the facts given ''"in the following pages have been 

 published in scientific papers which have appeared in the 

 last ten years. Some of them, however, are the result of 

 personal investigations not as yet published. A list of the 

 more important recent references to literature upon milk 

 bacteria is given at the close of the text. Wherever it seemed 

 to be necessary references to this literature have been inserted 

 in the body of the text. 



In the last chapter are given the methods of bacteriological 

 analysis in use at the present time, but, since some of these 

 are admittedly unsatisfactory in certain respects, it is quite 

 likely they may be replaced by better ones in the near future. 

 The growing appreciation of the necessity of bacteriological 

 study of market milk has made it desirable to insert careful 

 directions for laboratory work, even though recognizing that 

 these may not long remain the best methods of laboratory 

 technique. 



MIDDLETOWN, January, 1903. 



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