124 BACTERIA IN DAILY LIFE 



the bacterial and dirt contents of milk has been 

 clearly shown by actual investigation. A German 

 scientist has made a special study of the subject, 

 and has determined in a large number of milk 

 samples the amount of foreign impurities present 

 per litre, and the accompanying bacterial popula- 

 tion per cubic centimetre. 



The following results may be taken as typical 

 of those obtained : in milk containing 36-8 milli- 

 grammes of dirt per quart as many as 12,897,600 

 bacteria were present per cubic centimetre ; in 

 cleaner samples, with 20*7 milligrammes of dirt 

 per quart, the number of bacteria fell to 7,079,820 ; 

 whilst in a still more satisfactory sample, contain- 

 ing 5*2 milligrammes of dirt per quart, there were 

 3,338,775 bacteria per cubic centimetre. 



Such results indicate how important a factor is 

 scrupulous cleanliness in milking operations in 

 determining the initial purity of milk, for there is 

 no doubt that bacterial impurities in milk are in 

 the first instance, to a very great extent, controlled 

 by the solid impurities present. 



I do not know of any determinations which have 

 been made of the actual amount of such solid 

 impurities present in our public milk-supplies, but 

 such estimations have been made in many of those 

 belonging to large cities in Germany. Thus, Pro- 

 fessor Renk found in a litre of milk supplied to 



