OUTLINES OF DAIRY BACTERIOLOGY A CONCISE MANUAL FOR THE USE OF STUDENTS IN DAIRYING

OUTLINES OF DAIRY BACTERIOLOGY A CONCISE MANUAL FOR THE USE OF STUDENTS IN DAIRYING BY H. L. RUSSELL DEAN OF THE COLLEGE OF AGRICULTURE, UNIVERSITY OF WISCONSIN EIGHTH EDITION THOROUGHLY REVISED MADISON, WISCONSIN H. L. RUSSELL 1907 COPYRIGHTED 1905 BY H. L. RUSSELL STATE JOURNAL PRINTING COMPANY, PRINTERS AND STEREOTYPERS, MADISON, WIS. Transcriber`s note: Minor typos have been corrected. PREFACE. Knowledge in dairying, like all other technical industries, has grown mainly out of experience. Many facts have been learned by observation, but the why of each is frequently shrouded in mystery. Modern dairying is attempting to build its more accurate knowledge upon a broader and surer foundation, and in doing this is seeking to ascertain the cause of well-established processes. In this, bacteriology is playing an important rôle. Indeed, it may be safely predicted that future progress in dairying will, to a large extent, depend upon bacteriological research. As Fleischmann, the eminent German dairy scientist, says: "The gradual abolition of uncertainty surrounding dairy manufacture is the present important duty which lies before us, and its solution can only be effected by bacteriology." It is therefore natural that the subject of Dairy Bacteriology has come to occupy an important place in the curriculum of almost every Dairy School. An exposition of its principles is now recognized as an integral part of dairy science, for modern dairy practice is rapidly adopting the methods that have been developed as the result of bacteriological study. The rapid development of the subject has necessitated a frequent revision of this work, and it is gratifying to the writer that the attempt which has been made to keep these Outlines abreast of bacteriological advance has been appreciated by students of dairying. While the text is prepared more especially for the practical[Pg iv] dairy operator who wishes to understand the principles and reasons underlying his art, numerous references to original investigations have been added to aid the dairy investigator who wishes to work up the subject more thoroughly. My acknowledgments are due to the following for the loan of illustrations: Wisconsin Agricultural Experiment Station; Creamery Package Mfg. Co., Chicago, Ill.; and A. H. Reid, Philadelphia, Pa. H. L. RUSSELL. UNIVERSITY OF WISCONSIN. [Pg v] CONTENTS. CHAPTER I. Structure of the bacteria and conditions governing their development and distribution 1 CHAPTER II. Methods of studying bacteria 13 CHAPTER III. Contamination of milk 19 CHAPTER IV. Fermentations in milk and their treatment 62 CHAPTER V. Relation of disease-bacteria to milk 82 Diseases transmissible from animal to man through diseased milk 84 Diseases transmissible to man through infection of milk after withdrawal 94 CHAPTER VI. Preservation of milk for commercial purposes 102 CHAPTER VII. Bacteria and butter making 134 Bacterial defects in butter 156 CHAPTER VIII. Bacteria in cheese 160 Influence Of bacteria in normal cheese processes 160 Influence of bacteria in abnormal cheese processes 182 [Pg 1] CHAPTER I. STRUCTURE OF THE BACTERIA AND CONDITIONS GOVERNING THEIR DEVELOPMENT AND DISTRIBUTION. Before one can gain any intelligent conception of the manner in which bacteria affect dairying, it is first necessary to know something of the life history of these organisms in general, how they live, move and react toward their environment. Nature of Bacteria. Toadstools, smuts, rusts and mildews are known to even the casual observer, because they are of evident size. Their plant-like nature can be more readily understood from their general structure and habits of life. The bacteria, however, are so small, that under ordinary conditions, they only become evident to our unaided senses by the by-products of their activity. When Leeuwenhoek (pronounced Lave-en-hake) in 1675 first discovered these tiny, rapidly-moving organisms he thought they were animals. Indeed, under a microscope, many of them bear a close resemblance to those minute worms found in vinegar that are known as "vinegar-eels." The idea that they belonged to the animal kingdom continued to hold ground until after the middle of the nineteenth century; but with the improvement in microscopes, a more thorough study of these tiny structures was made possible, and their vegetable nature demonstrated. The bacteria as a class are separated from the fungi mainly by their method of growth; from the lower algae by the absence of chlorophyll, the green coloring matter of vegetable organisms.[Pg 2] Structure of bacteria. So far as structure is concerned the bacteria stand on the lowest plane of vegetable life. The single individual is composed of but a single cell, the structure of which does not differ essentially from that of many of the higher types of plant life. It is composed of a protoplasmic body which is surrounded by a thin membrane that separates it from neighboring cells that are alike in form and size. Form and size. When a plant is composed of a single cell but little difference in form is to be expected. While there are intermediate stages that grade insensibly into each other, the bacteria may be grouped into three main types, so far as form is concerned. These are spherical, elongated, and spiral, and to these different types are given the names, respectively, coccus, bacillus and spirillum (plural, cocci, bacilli, spirilla) (fig. 1). A ball, a short rod, and a corkscrew serve as convenient models to illustrate these different forms. Fig. 1. Different forms of bacteria. a, b, c, represent different types as to form: a, coccus, b, bacillus, c, spirillum; d, diplococcus or twin coccus; e, staphylococcus or cluster coccus; f and g, different forms of bacilli, g shows internal endospores within cell; h and i, bacilli with motile organs (cilia). In size, the bacteria are the smallest organisms that are known to exist. Relatively there is considerable difference in[Pg 3]size between the different species, yet in absolute amount this is so slight as to require the highest powers of the microscope to detect it. As an average diameter, one thirty-thousandth of an inch may be taken. It is difficult to comprehend such minute measurements, but if a hundred individual germs could be placed side by side, their total thickness would not equal that of a single sheet of paper upon which this page is printed. Manner of Growth. As the cell increases in size as a result of growth, it elongates in one direction, and finally a new cell wall is formed, dividing the so-called mother-cell into two, equal-sized daughter-cells. This process of cell division, known as fission, is continued until growth ceases and is especially characteristic of bacteria. Cell Arrangement. If fission goes on in the same plane continually, it results in the formation of a cell-row. A coccus forming such a chain of cells is called strepto- ... - tailieumienphi.vn