354 BOARD OF AGRICULTURE. [Pub. Doc. 



spirillum. These minute plants are of course absolutely in- 

 visible to the naked eye. In fact their average diameters 

 may be said to be one thirty-thousandth of an inch. The 

 elongated form have an average lenoth of from .0004 to .001 

 of an inch. 



Bacteria reproduce themselves by division and by spores. 

 By division is meant that a single plant develops a cell wall 

 within itself, and very shortly separates into two plants. 

 Spores are small round bodies formed within the plant, which 

 are thrown oft", and, under suitable conditions of heat and 

 moisture, rapidly develop into full-grown bacteria. Bacteria 

 multiply with wonderful rapidity. Many species, under 

 suitable conditions, will reproduce themselves within half an 

 hour. 



Bacteria find their way into milk as soon as drawn. They 

 fall in from the body of the cow, from the hands and clothes 

 of the milker, and from the dust of the air. Under the most 

 cleanly conditions large numbers of bacteria are found in 

 milk, while when the conditions are reversed, the number is 

 marvellously increased. It may be said that one twenty- 

 eighth of an ounce of milk has been found to contain from 

 6,000,000 to 170,000,000 bacteria. Bacteria develop most 

 rapidly at a temperature of 100° F., and their development 

 is checked the nearer the temperature is kept to the freezing 

 point. 



Changes in Pure Milk. 



Sour Milk. — One class of bacteria feeds upon the milk 

 sugar of the milk, and as a result lactic acid is formed. This 

 acid gives the milk its sour taste, and causes at the same 

 time the casein. or curd to separate out. The dirtier the ani- 

 mals, stables, milker and milk vessels, the larger the number 

 of bacteria that will find their way into the milk, and the 

 more quickly will the milk become sour. Milk sours more 

 rapidly in hot weather, because the temperature is better 

 suited to the rapid development of the bacteria. 



Bitter milk is sometimes due to improper food, or condi- 

 tion of the animal, and also to certain bacteria, which, having 

 gained access to the milk, attack the casein and decompose 

 it, producing butyric acid, peptones or other substances. 



