348 STATE BOARD OF AGRICULTURE 



Tlie investigatioDs of Forster, Demau and Bonhoff demonstrated that the tubercle 

 bacillus is killed liy the action of heat applied at 



50° C. (131° F.)for4hrs 

 60° C. (140° F.) for 1 hr. 

 65° C. (149° F.)for 15 min 

 79° C. (158° F.)for 10 min. 

 ^ 80° C. (196° F.) for 5 min. 



90° C. (194° F.)for 2 min. 

 95" C. (203° F.) for 1 min. 



Yersen by the use of the culture method has stated that the tubercle bacillus ex- 

 posed to the heat of 



55° C. (131° F.) for 10 minutes grew in 10 days. 



60° C. (140° F.) " " " 22 " 



70° C. (158° F.) " " and above failed to grow at all 



In an article by GrifHth on the pasteurization of milk, the assumption is made 

 that the tubercle bacillus is killed at 68° C. (15G° F.) to 70° C. (158° F.), and follows 

 the views of Bitter and Freeman, each of whom recommended 68° C. (156° F.) to 

 69° C. (159° F.) for pasteiu'izing purposes. Griffith, however, calls special atreu- 

 tion to the care necessary to proper pasteurization. Here he has certainly detected 

 one grave source of error. Pasteurization under no circumstances can be accom- 

 plished in a haphazard manner. 



Sternberg has given his Avork on the killing of the tubercle bacillus by heat. He 

 has found that the bacillus heated for 



10 minutes at 90° C. is killed. 



10 " " 80° C. 



10 " " 60° C. 



10 " "50° C. is not killed. 



The wide differences noticeable in the review of the above experimenters may 

 apparently be difficult to adjust, yet a possible reconciliation may be forthcoming by 

 a sttidy of the different methods employed and the various strengths of the virus 

 used. 



A comparative experimental study of the same virus under all the different meth- 

 ods in practice wotild be necessary for a satisfactory solution of the former ques- 

 tion. This is not a part of our work. Woodhead similated the methods customarily 

 used, but they were unreliable in his hands. On the statement of other investi- 

 gators, the methods in vogue are regarded as effective and satisfactory. If the 

 manner of determination has led to opposite views of the effectiveness of pasteuriza- 

 tion, some method will have to be devised by which uniform results may be ob- 

 tained and ordinary methods of pastettrization unquestioualtly settled. The ther- 

 mal death point in "Woodhead's studies was determined under as natural condi- 

 tions as it would seem possible, yet there may be errors arising from these very 

 conditions. Others have used the germ under artificial cultivation. This may in- 

 troduce grave errors, because the tubercle bacillus does not thrive the same under 

 artificial cultivation as under natural. What influence the manner of determin- 

 ing the thermal death point of the tubercle bacillus has upon the important meth- 

 ods of pasteurization in vogue, cannot be staled in definite terms. It must be set- 

 tled by further work. 



The tubercle bacillus is generally conceded to possess different degrees of dura- 

 bility, concerning which definite knowledge is available. There is strong evidence 

 that certain forms of the bacillus react differently than other forms. In sporogeuic 

 bacteria, there are always two forms to be considered, the sporeless forms and the 

 forms with spores, the thermal death points of which are widely separated. Again, 

 it is believed that spores, we will say, under different stages of development, pos- 

 .sess greater or less durability. Accordingly, when it is desired to determine the 

 thermal death-point of any species of bacteria, instead of establishing fast lines 

 which may be followed in full faith, there must constantly be some indefiniteness. 

 This is truer of spore forming bacteria than the sporeless kind. Now the tubercle 

 bacillus is usually regarded as a spore forming bacillus, and his spore nature is so 

 meagerly known that it is practically impossible to differentiate the two forms of 

 this germ; consequently it is nofstrange that variations in the results of determin- 

 ing the thermal death point should occur. This seems the more plausible wny of 



