24 GENERAL CONDITIONS AFFECTING BACTERIA IN MILK 



this country, have furnished results of such investigation. We have 

 ourselves made a very large number of bacterial examinations of 

 the air of byres, both during molecular disturbance and otherwise, 

 and have isolated a large number of micro-organisms. A statement 

 concerning these will be found elsewhere. 



During treatment or preparation the main source of pollution 

 arises from the air of the dairy or the apparatus used for separa- 

 tion. We have examined dairy air and dairy utensils and have 

 found them far from bacteriologically pure. On the ordinary farm 

 it is difficult to cleanse utensils thoroughly, and it is the custom to 

 leave the milk exposed to the air of the dairy. Through these 

 two sources it is remarkable how many bacteria gain access to the 

 milk. But in efficiently and well-conducted dairies both these 

 agencies should be reduced to a minimum.^ 



The risks in transit differ according to many circumstances. 

 Probably the commonest source of contamination is in the use of 

 unclean utensils and milk-cans. Any unnecessary delay in transit 

 affords opportunity for multiplication ; particularly is this the case 

 in the summer months, for at such times all the conditions are 

 favourable for an enormous increase of any extraneous germs which 

 may have gained admittance at the time of milking. The milk 

 churns are left standing on railway platforms unprotected from the 

 sun or dust. The churns may be insufficiently closed, and as a rule 

 are neither locked or sealed. Thus we have {a) the milk itself — 

 a perfect pabulum for bacteria ; {b) a more or less lengthened railway 

 journey or period of transit, giving ample time for multiplication ; 

 {c) the favourable temperature of summer heat. 



The period occupied by transit depends, of course, upon the 

 size of the community to be supplied. The great growth of cities 

 has widened the area from which milk is obtained, so that at the 

 present time it may be said that most of the milk consumed in 

 large cities has undergone a more or less lengthened railway 

 journey, and must have been kept, say from twelve to twenty-four 

 hours, before it reaches the consumer. The milk supply of London 

 and Paris is in each case derived from a very wide area.^ In 

 London the milk is delivered by rail at the stations about 2 A.M. 



^ As a result of experiment on an extended scale (published since the above 

 was written), Delepine holds that infection of the milk at the farm or through 

 vessels infected at the farm and used by the farmers for the storage and carriage 

 of milk are of paramount importance, and play a much greater part in the 

 bacterial pollution of milk than infection in the house of the consumer. — Jour, 

 of Hygiene^ i903) vol. iii., No. r, pp. 79-87. 



2 See also /our. Roy. Stat. Soc, 1892, pp. 244-273. 



