CHAPTER III. 



MILK IN ITS RELATION TO MICRO-ORGANISMS. DAIRYING AND 

 BACTERIOLOGY. 



36. The Bearing of Bacteriological Research on Dairying. Long 

 before it was known that all fermentation and decomposition were 

 caused by micro-organisms, the practice of dairying prescribed the 

 greatest cleanliness in the treatment of milk and the great im- 

 portance of always providing good pure air in all dairies; it showed 

 the danger of exceeding a certain temperature, and recommended in 

 cheese-making a careful regulation of the percentage of moisture in 

 the cheese. The real reasons of these precautions were not known 

 at that time, but experience taught that their observance was the 

 best security against certain injuries to which dairy products were 

 liable. We now know that uncleanliness leads to a rapid development 

 of all micro-organisms, that musty stagnant air is heavily laden 

 with spores of fungi and bacteria, that the activity of growth of 

 these small organisms is influenced by the temperature, and that in 

 general the damper and softer the fermenting mass is, the more 

 rapidly does the development of fermentation take place. It is a 

 fact that many bacteria which act as carriers of deadly infectious 

 diseases, or as the creators of poisonously acting substances, can live 

 in milk and render it poisonous. It has further been proved that 

 certain bacteria cause the so-called spontaneous coagulation of milk, 

 that others can exercise a disturbing influence on the creaming of 

 milk and on the preparation of butter, and that other micro- 

 organisms can cause the ripening of cheese in quite undesired ways. 

 Just as, in dairy practice, it is desirable on the one hand to war 

 against dangerous or unfavourable processes caused by bacteria, so 

 on the other hand it is desirable to promote the action of certain 

 kinds of fission fungi. For example, some are not only absolutely 

 necessary for the process of cream souring, required in the pro- 

 duction of fine butter, but also for the inception and development 

 of the ripening processes to which the different kinds of cheeses 

 owe their characteristic properties. The undisturbed and regular 

 development of dairy manufactures depends upon the successful 



