March, 1922. 



SCIENTIFIC AGRICULTURE 



213 



The Spoiling of Milk 



By Wilfrid iSadler, M.Se. and Marion J. Mounce, B.A., B.«.A. 

 Department of Dairying, University of British Columbia, Vancouver. 



The spoiling of milk is primarily due to 

 the activities of bacteria. Other factors, 

 agencies and conditions associated with 

 this spoilage are either contributory to the 

 l)acterial activities or are of secondary 

 importance. The researches of Moore & 

 Ward, (1) Harrison, (2) Savage, (3) 

 Harrison & Savage, (4) Bergey, (o) Conn 

 Esten & Stocking, (6) Harding & Wilson, 

 (7) Evans, (8) and others on the bacterial 

 content of the normal udder of healthy 

 cows, have shown that milk as secreted may 

 be sterile; but that in the udder itself a 

 limited flora persists. The numbers and 

 types of bacteria found in the milk drawn 

 at the beginning of and during the early 

 stages of milking, are variable, even when 

 aseptic precautious are taken ; for there is 

 the possibility of external contamination of 

 the udder via the teat canal. In the strip- 

 pings, or milk drawn during the later stages 

 of the operation, the bacterial content is 

 low, the flora is more constant, and the 

 types are well defined. Certain strains of 

 tiie baetei ia which have been isolated from 

 the udder have a specific action in milk; 

 but the causative organisms of milk fer- 

 mentations in a major sense are chiefly 

 those which obtain an entrance during and 

 subsequent to the operations of milking. It 

 would appear therefore, that, in the main, 

 the bacterial contamination of milk is 

 preventable; and it would necessarily fol- 

 low that the spoiling of milk is prevent- 

 able just in so far as we are successful in 

 preventing and controlling the entrance 

 and multiplication of bacteria. The ex- 

 tent to which preventable measures are 

 possible in actual practice is a questi(m of 

 fundamental importance to the dairy 

 farmer, to public health authorities, and 

 to the community at large ; for the rapidity 

 with which milk spoils, decides the limit 

 of its 'period of usability.' 



In the work done on the milk supply of- 

 the City of Montreal by Harrison, Savage 

 and Sadler (9) some 1500 examinations 

 were made. Taking one phase of the in- 

 vestigation, it was found that out of 900 

 samples, 600 samples represented milk 

 which could not have been sold in New 



York, Boston or Chicago, on account of the 

 high bacterial content. In other words, 

 had the law in Montreal been the law in 

 exi.stence in the cities mentioned, the milk 

 represented by 600 of the 900 samples ex- 

 amined would have been lost to the com- 

 munity; that is, the 'period of usability' 

 of the milk was so limited that it would 

 not have provided for the time expiring 

 between production and marketing. There 

 is reason for believing that to-day the con- 

 ditions pertaining to the milk supply of 

 Montreal have been improved to a marked 

 degree. 



During the war,, the Institute for Dairy- 

 ing Research, University College, Reading, 

 was requested by the Imperial Government 

 to enquire as to the losses in milk due to 

 spoilage. The milk supply from two dis- 

 tricts producing 90,000,000 gallons and 

 75,000,000 gallons per annum respectively 

 was investigated. It was found by Sten- 

 house Williams (10) that at the time the 

 milk should have been available for use 

 by the consumer, no less than one per cent, 

 or 1,650,000 gallons had spoiled. At pri- 

 ces current at that time, the financial loss 

 is to be computed at $7,000,000. Not only 

 was there the loss of money, but the loss 

 in terms of food, and as concerns the in- 

 fant and the child, the loss of a food for 

 which there is no substitute. More recent 

 researches undertaken by Freear, Buckley 

 and Williams, (11) of the same Institute, 

 have demonstrated the inter-relationship 

 of conditions on the farm, age of milk and 

 temperature at which the milk had been 

 kept prior to its arrival in the laboratory, 

 total bacterial content, and percentage of 

 samples containing organisms of the colon- 

 aerogenes group in 1 cc. of the milk at the 

 time of examination. Further, the periods 

 occupied by the milk in forming the clot 

 when held at specific temperatures in the 

 laboratory have been correlated with .the 

 aforementioned. Wlien produced under 

 satisfactory conditions, 71 of the 73 .sam- 

 ples of milk examined contained' 10,000 

 bacteria or less per ec; and 8 of the sam- 

 ples were found to have organisms of the 

 colon-aerogenes group in 1 cc. In the milk 



