EXPERIMENT STATION BULLETINS 347 



"Temperature 2J min., 5 min., 10 min., 15min., 20 min., 30 min., 40 min., 45 min., 1 hr. 

 60^C. (140^ F.) + + 



65'='C. (149° F.) -f + 



79°C. (158° F.) + + + 



75°C. (167° F.) + + -t- 



80°C. (176° F.) + + 



+ = Positive. 



— = Negative. 



= No experiments were made." 



Even in the feeding experiments, there is much which points tu tlie durability of 

 tuberculous virus. This table is worthy of the gravest consideration, for it indi- 

 cates the possible harm arising from tuberculous milk which has neither been 

 thoroughly nor properly pasteurized. Before giving any further attention to the 

 above results, it is desirable to quote still more of his experiments in scalding milk. 

 "Experiments were made as to the effect of the ordinary process of 'scalding' milk 

 in which the milk in the earthenware jar or tin pan is placed in another pan con- 

 taining a quantity of water, which is then brought to the boiling point. It was 

 found that, under these circumstances, the temperature of the milk of the upper 

 part raised much more rapidly than that of the lower part. In one experiment, 

 after the milk had been on the fire for fourteen minutes, the temperature at the 

 top was 71.1° C. (160° F.), while at the bottom is was 50° C. (133° F.); at the end 

 of twenty-six minutes, the temperature at the top was 92° C. (198° F.). at the 

 bottom, 83.5° C. (182° F.). In another experiment, with a stronger flame, these dif- 

 ferences were less marked. These experiments clearly proved that the mere scalding 

 of milk by bringing the outside water up to the boiling point, was quite inadequate 

 to sterilize tuberculous uiilk." 



The following directions are given by Woodhead for tlie pasteurization of milk 

 when it is desired to arrest souring or v^-hen it may he necessary to make use of 

 milk from an unknown or suspicious source: (1.) "The quantity of milk should 

 never be more than the quantity of cold water by which it is surrounded; it is, in 

 fact, an advantage to have a larger bulk of water than of milk to allow for evap- 

 oration. (2.) The milk should not be covered in and should be stirred from time 

 to time, but the water may with advantage be covet'ed, in order to prevent evap- 

 oration; this of course is arranged for, in special milk sterilizing pans. (3) The 

 water should be boiled over a good brisk flame, in order that the best results may 

 be obtained, and the heating process should be continued until the temperature 

 throughout the milk has risen to from 88° C. (190° F.) to 92° C. (198° F.); in most 

 cases this takes place at the end of nbout twenty-five minutes, but in order to be 

 perfectly safe it may be recommended that every quart of milk treated in this 

 fashion, should be heated for half an hour— that is, for about twenty minutes after 

 the water in the outer pan has begun to boil.' 



The most striking feature of Woodhead's elaborate experiments is. perhaps, the 

 high thermal death point required for the killing of the tubercle bacillus. The 

 ordinary methods employed in pasteurizing milk Avould be regarded by him as 

 unsafe. From others, however, different views are obtained. 



Freeman says: "As far as the ordinary bacteria are concerned, pasteurization 

 at 140° F. gives almost as good results as that of 167° F. The milk is freed from 

 almost all the living germs, and those pathogenic bacteria which are most likely 

 to cause disease are also destroyed. The only pathogenic bacterium which is not 

 destroyed by a short exposure to a temperature of 140° F. or less is the bacillus 

 tuberculosis", but there is evidence that this micro-organism is destroyed by a tem- 

 perature of less than 140° F. of sufficient duration." The evidence of the most 

 recent observers, he says, seems to him sufficient to conclude that a temperature 

 of 140° F. kept up for fifteen minutes is sufficient to kill lincillus tuberculosis, and 

 he recommends pasteurization at or between 149° F. or 167° F. 



A pasteurizing apparatus has been tested by MacFadyean and Hewlett, which 

 consists of a coil of pipe heated to 68°-72° C. (1.53°-160° F.) and requiring thirty sec- 

 onds for the milk to pass through. This would be the same practically as heating 

 the milk at 68°-72° (1.53°-160° F.) for thirty seconds. To test whether the tubercle 

 bacillus was killed by this means, they took tuberculous, sputum dried over sul- 

 phuric acid, powdered it and mixed it in sterilized milk. Two guinea pigs inocu- 

 lated with 2 c. e. each before pasteurizing died exactly a month after. The glands, 

 spleen, mesentery, liver, lungs and peritoneum were riddled with tubercle. Three 

 guinea pigs inoculated each with 2 c. c, after pasteurization, showed no trace of 

 tubercle upon careful post-mortem. 



