CHEMICAL TESTS OF MILK 211 



Care must be taken to thoroughly cleanse and sterilize the 

 outside of the tin before opening, while the instrument to open 

 the tin, which most conveniently is an ordinary tin-opener, 

 must be sterilized before use. 



The records of bacteriological examinations of milk are 

 not very numerous. The following will give a good idea of the 

 results likely to be obtained. 



Sandilands^ made some experiments upon the rate of 

 multiplication of bacteria in condensed milk, and the liability 

 of condensed milk to decomposition. He used Nestle's 

 sweetened whole milk in all the experiments. He did not 

 enumerate the number of bacteria in the fresh samples, but 

 only after incubation at 22° and 37° C. respectively. Com- 

 pared with cow's milk he found the bacterial content of 

 condensed ISTestl^'s milk very low, and it remained low for a 

 week or more at the ordinary summer temperature of 70^ F. 

 (21° C). The viscidity of the milk and the presence of added 

 sugar are probably the two factors which combine to inhibit 

 bacterial growth. 



Newsholme ^ records the results of the bacteriological 

 examination of twelve different samples of condensed milk 

 carried out by Dr. Heggs. The samples were examined when 

 opened, and again after the tins had been opened and exposed 

 to the air, in the laboratory, for some days. The initial 

 number of bacteria present varied from 230 to 70,940 per c.c. 

 on the gelatine -plates grown at 20° C, and from 120 to 

 44,200 per c.c. on the agar-plates at 37" C. The duration of 

 exposure to the air after opening varied from three to eleven 

 days. In no case was the number of bacteria very large even 

 after eleven days' incubation. These results are in agreement 

 with those of Sandilands, and show the comparative unsuita- 

 bility of condensed milk as a medium for bacteria compared 

 with ordinary milk. 



Klein ^ examined 3 2 samples of 11 different brands 

 of sweetened condensed milk. All contained bacteria, the 

 number in O'l grm. varying from 13 to over 2000 (upon 

 agar at 37" C). Streptococci were present in O'l grm. in 



1 Journ. of Hygiene, 1906, vi. p. 77. 

 2 Ibid. p. 139. 

 3 Puhlie Health, 1909, xxii. p. 222. 



