32 



Pasteurisation of Milk and Cream. 



determination of this point. The plan of these investigations 

 is described in the number of the Journal referred to above- 

 Briefly, the results showed that in milk pasteurised at 

 140 deg. Fahr. for either 15 or 30 minutes the cream rose 

 as quickly and as completely as in the case of normal milk I 

 that the creaming property was normal in samples pasteurised 

 at this temperature for 60 minutes ; that there was no differ- 

 ence in the keeping quality of milk heated to 140 deg. for 

 15 or 30 minutes and milk heated to 155 deg. for 15 minutes 

 — these results were further confirmed by a bacteriological 

 examination — and that there was no difference between the 

 consistency of raw cream and that heated to 140 deg. for 

 30 minutes. 



It was found, therefore, that a temperature of 140 deg. 

 Fahr., if maintained for a sufficient period, was effective in 

 destroying these bacteria, and the point which remained 

 for determination was how long an exposure at this tempera- 

 ture would be requisite to destroy the tubercle bacillus. Dr. 

 Theobald Smith's researches had shown that when the milk 

 was agitated during pasteurisation, the period of exposure 

 could be materially reduced below 60 minutes, wmich had 

 been previously considered necessary ; and Messrs. Farring- 

 ton and Russell undertook to re-test this point under factory 

 conditions. These tests were made during 1900, and the 

 results have been communicated by Dr. Russell to a meeting 

 of the American Public Health Association at Indianapolis. 

 The milk to be tested was heavily charged with living 

 tubercle bacilli, and injections of the pasteurised milk were 

 injected intraperitoneally into guinea-pigs. In all cases the 

 milk which had not been heated produced tuberculosis ; the 

 milk exposed to a temperature of 140 deg. for only five 

 minutes also produced tubercle ; but no trace of the disease 

 could be found in the guinea-pigs injected with milk which 

 had been kept at this heat for ten minutes or longer. The 

 conclusions arrived at by Dr. Russell are as follows :— 



1. An exposure of tuberculous milk in a tightly-closed commercial pasteuriser 

 for a period of ten minutes destroyed in every case the tubercle bacillus as- 

 determined by the inoculation of such heated milk into susceptible animals 

 like guinea pigs. 



