BACTERIA IN MILK AND ITS PRODUCTS - 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. 268466 CHAPTER CHAPTER CHAPTER CHAPTER CHAPTER CHAPTER TABLE OF CONTENTS. I. II. III. IV. V. VI. CHAPTER VII. CHAPTER VIII. CHAPTER IX. PAG THE NATURE OF BACTERIA . . . .17 SOURCES OF BACTERIA IN MILK . . -32 TYPES OF MILK BACTERIA, . . . .61 GROWTH OF BACTERIA IN MILK . . ,97 MILK BACTERIA AND HEALTH . . . 108 How SHALL THE CONSUMER OF MILK PROD- UCTS BE PROTECTED 140 BACTERIA IN BUTTER ..... 179 BACTERIA IN CHEESE BACTERIOLOGICAL ANALYSIS OF MILK vii 220 251 BACTERIA IN MILK AND ITS PRODUCTS. CHAPTER I. THE NATURE OF BACTERIA. THE last fifteen years have seen a very great change tak- ing place in the methods of handling milk products. These changes have affected not only the handling of milk distributed for public consumption, but also the manufacture of butter, and they are rapidly producing improvements in the manufacture of cheese. The modifications of dairy meth- ods have been more rapid in the last twenty years than ever before, and we may almost say that greater changes have taken place within this short time than in the previous two centuries. A variety of new conditions and new discoveries have contributed to this end, but nothing has had a greater influence than the knowledge which has developed concern- ing the nature of bacteria and their relation to milk. Dairy bacteriology has to a large extent revolutionized, modern dairying...