BACTERIA IN FOODS 213 



As regards the later effect of the process, he states that in 

 fifteen samples of pasteurised milk examined from Novem- 

 ber to December nine of them revealed no organisms, or so 

 few that they might almost be regarded as sterile; in those 

 samples examined after January the lowest number was 100 

 germs per cc, while the average was nearly 5000. With 

 the pasteurised cream a similar condition was to be ob- 

 served. 



Dr. Hewlett ' defines pasteurisation briefly as heating the 

 milk to 68° C. for twenty or thirty minutes, and this treat- 

 ment he quotes as destroying 99.75 per cent, of the total 

 number of organisms. Bitter's table of results at 158° F. 

 bears out the same : 



Before Pasteurisation. After Pasteurisation. 



No. of Bacteria in 10 Drops. No. of Bacteria in 10 Drops, 



I 102,600 2 — 3 



2 251,600 30 — 40 



3 25,000 3—5 



4 37,500 2—5 



5 94,000 2 



BACTERIA IN MILK PRODUCTS 



Cream is generally richer in bacteria than milk. Set cream 

 contains more bacteria than separated ex tdLva^ but germs are 

 abundant in both. Yet whilst it is true that cream contains 

 a large number of bacteria, it must be pointed out that the 

 butter fat in cream is a less suitable food for organisms than 

 is the case with milk. Hence the fermentative changes set 

 up in cream are of less degree than in milk, particularly so 

 if separated from the milk. Butter-milk and whey vary 

 much in their bacterial content. Butter necessarily follows 

 the standard of the cream. But as the butter fat is not 

 well adapted for bacterial food, the number of bacteria in 



^A Manual of Bacteriology, Clinical and Applied, p. 397. 



