118 THE ENUMERATION OF BACTERIA IN MILK 



same in two cases." The averages of the whole series (omitting 

 the samples counting in millions) were 299,000 for the twenty- 

 four hour count and 147,000 for the twenty-four hour count. 

 This gives a ratio of 2.03 : 1. It is obvious that no constant 

 factor can be employed for the ratio of the twenty-four hour 

 count to the forty-eight hour count as this will vary with the 

 bacterial flora. For the same reason the results obtained with 

 the use of different media are not comparable although they 

 usually vary in the same direction. This is well illustrated by 

 the results given in Table XLIX which shows a comparison 

 between standard agar and gelatine. 



It will be seen that when the bacterial count is low, the dif- 

 ference between the gelatine and agar count is but small, 

 and, although the gelatine medium usually gives the higher 

 result, this is not an invariable rule ; the agar occasionally gives 

 a higher count, but this, in the author's experience, only occurs 

 in a small minority of cases and as the bacterial count increases, 

 the ratio of the gelatine count to the agar count usually becomes 

 greater. 



That the addition of 1 per cent of lactose to both nutrient 

 gelatine and agar, favours more rapid reproduction is shown in 

 Table L. 



Table L 



