300 



MILK AND ITS HYGIENIC RELATIONS 



milk in bulk shall reach the average temperature aimed at, some 



form of stirring must be resorted to in order to keep the milk heated 



evenly as it passes up to the required temperature. It will of 



necessity have to pass through various pieces of apparatus, and a 



number of forms of such apparatus involve a coil of somewhat 



narrow dimensions through which the milk is made to circulate. 



The purpose of this coil is to cool the milk either by means of cold 



or iced water, or sometimes by running the milk which is to be 



pasteurised, and is cool, through the coil, thus saving some heat. 



If the object of pasteurisation is to be attained, absolute cleanliness, 



and if possible sterility, must be secured in the apparatus used, 



otherwise there is a danger that the milk may acquire as many 



bacteria from the pasteurising plant as it loses in the process of 



heating. The net result, therefore, is that little or no advantage 



has been gained by the pasteurisation. 



The figures of Pennington and McClintock (given below) are of 

 considerable interest in this connection, and show the recontamina- 

 tion of milk as a result of an unclean pasteurising plant. 



II 



These figures afford excellent examples of contamination by 

 dirty machinery. 



Another example of contamination in the process of condensa- 

 tion is given by Delepine in the course of his investigations upon 



