Bactériologie laitière pratique, prête à l'usage des étudiants, producteurs, et tous les intéressés par les problèmes de la relation du lait pour la santé publique . Milksoured à haute température donc contient généralement des handedlactic à gauche, tandis que l'acide qui tendent à aigri contient-handedacid^ droite. Ces faits sont d'specialimportance dans la fabrication du fromage que sera indiqué plus loin. RENNETFORMING PEPTONIZING et parfois les bactéries dairyman est un puzzledby,phénomène assez inhabituel pour qu'il trouve son caillage du lait, butnot devenir aigre, et il parle du phénomène de caillage doux.Il est susceptible d'oc

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Practical dairy bacteriology, prepared for the use of students, dairymen, and all interested in the problems of the relation of milk to public health . Milksoured at high temperatures there-fore commonly contains left-handedlactic acid, while that soured at lowtemperature contains right-handedacid.^ These facts are of specialimportance in cheese making as willbe noted later. PEPTONIZING AND RENNETFORMING BACTERIA At times the dairyman is puzzledby a somewhat unusual phenomenon, for he finds his milk curdling, butnot becoming sour, and he speaks ofthe phenomenon as sweet curdling.It is apt to occur in the fall orspring, when the food of the cattleis being changed. It is due to aclass of bacteria that have the powerof secreting certain chemical fer-ments very similar to those producedby the digestive glands of the stom-ach and intestine. Upon almost any gelatin plate madefrom milk (see page 280) there willbe found, in addition to the coloniesof lactic acid bacteria, a number of pits in which the gelatin isbeing dissolved or liquefied. This effect is produced by bacteria, and if a platinum needle be dipped into one of these pits and then. FIG. 21—^LIQUEFACTION OFGELATIN BY ENZYME-FORMING BACTERIA ^ Ferguson. Die spontane Zersetzung der Milch. Gottingen, 1902.Conn. Ann. Rep. Storrs. Exper. Sta., 1906. 40 PRACTICAL DAIRY BACTERIOLOGY. Stabbed into a gelatin tube, in a da;y or two it will be founii.that the bacteria thus inoculated are liquefying the gelatin, , as shown in figure 21. These bacteria do not liquefy agar, andcan, therefore, be best studied in gelatin. If these bacteria be inoculated into milk, they will usuallycurdle it in the course of a day or two; but they do not produceany acid, hence they act differently from the lactic acid bacteria.The curdling is actually brought about by a chemical fermentsecreted by the bacteria, which is very similar to rennet secretedby glands in the stomach of mammals, the material used bycheese makers to curdle their milk. Such c

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