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

s microscopes. For this reason, but little advance was made in the knowledge of these lower forms of plant life, until the introduction of culture methods, whereby a

al form, unless the medium in which they are grown is first freed from all pre-existing forms of germ life. To accomplish this, it is necessary to subject the nutrient medium to some method of sterilization, such as heat

any organic substance whether it is solid or fluid, provided the other essential conditions of growth are furn

ch, permits the separation of the different forms that may happen to be in any mixture. Gelatin is used advantageously because the majority of bacteria present wider differences due to growth upon this medium than upon any other. It remains solid at ordinary tem

vegetable and animal tissues. Skim-milk is of especial value in studying the milk bacteria and may be used in its natural cond

rowth (colony) derived from a single cell. Different forms react differently toward the gelatin, some liquefying the same, others

surface, or in the depth of the culture medium. These patches are called colonies and are composed of an almost infinite number of individual germs, the result of the continued growth of a single organism that was in the drop of milk which was firmly held in place when the gelatin solidified. The number of these colonies represents approximately the number of germs that were present in the milk drop. If the plate is not too thickly sown with these germs, the colonies will continue to grow and increase in size, and as they do, minute differences will begin to appear. These differences may be in the color, the contour and the texture of the colony, or t

g.

efying form that dissolves the gelatin; c and d,

are secured. These cultures then serve as a basis for continued study and must be planted and grown upon all the different kinds of media that are obtainable. In this way the sligh

bacteriology, as it is the only way in which it is po

nstant demand throughout all the different stages of the isolating process. For this purpose, it is essential tha

g.

Fine parallel filaments growing out into medium liquefying at surface; c, a rapid liquefying form; d, a gas-producing form that grows

fact, the two must go hand in hand. The examination reveals not only the form and size of the individual germs, but

s of anilin dyes as staining agents. These are of great service in bringing out almost imperceptible differences. The art of staining has been carried t

he germ may possess. Thus, the ability of any form to act as a fermentative organism can be tested by fermentation experiments; the property of causing disease, studied by the inoculation of pure cultures into animals. A great many different methods have been devised for the