x 9°5-] Cleanliness in Dairy Management. 137 



number of those minute forms of life known as germs, bacteria, 

 or microbes. If it were possible in ordinary practice to draw 

 milk from the udder without exposing it to bacterial contami- 

 nation, souring and other changes would not take place. 



Of the organisms which get into milk it may be said that 

 they belong to the smallest forms of plant-life, which find in 

 milk a very suitable food and a medium in which they 

 multiply rapidly, especially when it stands for a time in a 

 warm place after being drawn from the cow. There are many 

 species of these organisms, all of which are more or less distin- 

 guishable either by their form, habits of growth, or effects. 



Fig. I. Photograph of a gelatine plate Fig. 2.— Photograph of a gelatine plate 

 exposed for one minute in a badly exposed for one minute in a well 

 ventilated cow-shed. ventilated cow-shed. 



During active life an organism absorbs food through its cell 

 walls, and gives out a secretion or substance varying according to 

 the species. The secretions of these organisms have a peculiar 

 chemical action upon one or more of the constituents of the 

 milk which may affect the whole. For example, a lactic ferment 

 secretes a substance which acts on the milk-sugar, thereby pro- 

 ducing lactic acid ; this acid in turn acts on the casein, bringing 

 about a state of coagulation. Another species secretes a sub- 

 stance which acts directly on the casein, rendering it viscid, and 

 resulting in what is ordinarily known as ropy milk. The objec- 

 tionable flavours that are from time to time found in milk, 

 butter, or cheese, are also, as a rule, due to the particular bacterial 

 life existing therein. 



