METHODS COMMONLY USED IN HEATING MILK 301 



the fate of bacteria added to a sample of milk which was to 

 be condensed. He shows that a considerable increase in the number 

 of bacteria the increase being chiefly due to moulds occurred 

 in the course of the process, and he states that this may be attributed 

 to the presence of some bacteria and moulds in the delivery pipe 

 used to empty the vacuum pan. The conditions under which the 

 milk was manipulated were stated to have been excellent. 



The temperatures to which milk should be heated in order to 

 destroy certain forms of bacteria, both pathogenic and otherwise, 

 are considered in Chap. XVIII. But it may be stated that the 

 dangers of dirty apparatus or of ineffectual pasteurisation should 

 not be minimised. They have been shown to be real. In this 

 connection Chap. XV, section D, dealing with milk epidemics, may 

 be compared. 



These difficulties, and the dangers connected with commercial 

 pasteurisation, are dwelt upon by many authors who have written 

 upon the subject. Thus Savage points out that one of the 

 objections arises from the sale of milk which, owing to pasteurisa- 

 tion, is prevented from souring, and ' in practice probably often is 

 kept over a number of days. Old, stale milk may be sold as fresh 

 owing to the removal of most of the lactic acid bacilli. Such milk 

 will appear normal to sight and taste, but may be bacterially 

 highly dangerous. If used without statutory control, there can 

 be little doubt that the extensive use of pasteurisation would lead 

 to neglect of general sanitary conditions even more than is the 

 case to-day, under the belief that the pasteurisation would be an 

 efficient substitute for cleanliness. ... It is probable that much 

 commercial pasteurisation is inefficiently done. It is a procedure 

 involving an accurate adjustment of time and temperature, and 

 frequently being left to be performed by careless and unskilled 

 persons (the so-called " practical man " ), it is very unequally and 

 inefficiently done. If pasteurisation is to be allowed at all, it 

 should be controlled both as regards methods and apparatus. In 

 the writer's opinion, summing up the matter, pasteurisation is an 

 efficient and useful procedure which may be very valuable pending 

 satisfactory and radical improvement in the milk business as a 

 whole, but it is likely to be more harmful than beneficial unless the 

 practice is rigidly supervised, and the conditions under which 

 it may be employed regulated.' Rosenau, in his work upon 

 pasteurisation undertaken for the Hygienic Laboratory in Washing- 

 ton, says : ' One of the chief objections to pasteurisation is that 

 it promotes carelessness and discourages the efforts to produce 

 clean milk. It is believed that the general adoption of pasteurisa- 

 tion will set back improvements at the source of supply and 

 encourage dirty habits. It will cause the farmers and those who 

 handle the milk to believe that it is unnecessary to be quite so 

 particular, as the dirt that gets into the milk is going to be cooked 

 and made harmless/ 



