Outlines of Dairy Bacteriology, 8th edition / A Concise Manual for the Use of Students in Dairying

ffect dairying, it is first necessary to know something of the life history of t

Their plant-like nature can be more readily understood from their general structure and habits of life. The bacteria, however, a

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

mposed 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 co

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, respect

g.

, spirillum; d, diplococcus or twin coccus; e, staphylococcus or cluster coccus; f and g, different f

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 m

a new cell wall is formed, dividing the so-called mother-cell into two, equal-sized daughter-cells. This process

only two cells cohere, it is called a diplo-coccus (twin-coccus). If the second cell division plane is formed at right angles to the first, a cell surface or tetrad is formed. If growth takes pl

nd spores of fungi. By means of these structures which are endowed with greater powers of resistance than the vegetating cell, the organism is able to protect itself from the

motion. Motion is produced by means of fine thread-like processes of protoplasm known as cilia (sing. cilium) that are developed on the outer surface of the cell. By means of the rapid vibration of these org

constant. With the bacteria these differences are so slight that they alone do not suffice to distinguish distinctly one species from another. As far as these characters can be used, they are taken, but in addition, many characteristics of a physiologi

unfavorably. Certain conditions must prevail before development can occur. Thus, the organism must be supplied with an adequate and suitable food sup

nourishment from the living tissues of animals or plants. The first group comprise by far the larger number of known organisms which are concerned for the most part in the decomposition of organic matter. The parasitic group includes those which are the cause of

through the development of disease in the animal are parasites in the strict sense of the term. Most disease-producing species, as

neral matter. The nitrogen and carbon are most available in the form of organic compounds, such as albumino

before they can be appropriated. If nutritive liquids are too highly concentrated, as in the case of syrups and condensed milk, bacteria cannot grow therein, although all the necessary ingredients may be pr

mperature points, and generally nearer the maximum limit is the most favorable temperature for growth, known as the optimum. The temperature zone of most dairy bacteria in which growth occurs ranges from 40°-45° F. to somewhat above blood-heat, 105°-110° F., the optimum being from 80°-95° F. Many parasitic species

gen which they need from organic compounds such as sugar, etc., and are therefore able to live and grow under conditions where the atmospheric air is excluded. These are known as anaerobic. While some species grow strictly under one condition o

l at the optimum point, which is generally near the blood heat or slightly below (90°-98° F.), a single cell will form two cells in 20 to 30 minutes. If temperature rises much above blood heat rate of growth is lessened and finally ceases. Under ideal conditions, rapidity of growt

repress their development or destroy them. These act much more readily on the vegetating cell than on the more resistant spore. A thorough k

exposure to low temperatures will effectually destroy the vitality of bacteria, even in the vegetative condition. Numerous non-spore-bearing species remain alive i

he thermal death point. This limit is not only dependent upon the nature of the organism, but varies with the time of exposure and the condition in which the heat is applied. In a moist atmosphere th

ected. In the spore stage resistance is greatly increased, some forms being able to withstand steam at 210°-212° F. from one to three hours. If dry heat is employed, 2

pores retains its infectious properties for many months. Most of the dairy bacteria do not produce spores, and yet in a dry cond

cells that are reached by the sun's rays. Even diffused light has a similar effect, although naturally less marked. The ac

ust of necessity be antiseptic in their action, but not all antiseptics are disinfectants even when used in strong doses. Disinfectants have no place in dairy work, except to destroy disease bacteria, or preserve milk for analytical purposes. Corrosive sublimate or potassium bichromate are most frequently used for these purposes. The so-called chemical preservatives used to "keep" milk depend f

medium in which the bacteria may happen to live. Such changes are known, collectively, as fermentations, and are characterised by the production of a large amount of by-products, as a result

r, under the action of various organisms, sooner or later undergoes decay, and in different stages of these processes, acids, alkalies, gases and numerous

ivity of the cell is wholly suspended. These enzyms are not confined to bacteria but are found throughout the animal and plant world, especially in those processes that are concerned in digestion. Among th

of organic matter. Most of these enzyms react toward heat, cold and chemical poisons in a manner quite similar to the living cells. In one respect they are readily differentiated, and t

conditions permit of their growth, they are found everywhere, except in the healthy tissues of animals and plants. In the superficial soil layers, they exist in myriads, as here they have abundance of nour

o readily dislodged by wind currents that over land areas the lower strata of the air always contain them. They are more numerous in summer tha

obes. As the rain water percolates into the soil, it loses its germ content, so that the normal ground water, like the deeper soil layers, contains practically no bacterial life. Springs therefore are relatively deficient in germ l

dily infected. This is particularly true with reference to the intestinal tract, for in the undigested residue, bacterial activity is at a maximum. The result is that fecal matter contains eno