10 
bacteriologic technic in preparing this culture fluid. Whether whole 
milk or skimmed milk was used is stated in each instance. 
The test tubes in wdiich the infected milk was heated were open 
to the air, and scum formation was disregarded in all instances, my 
object being to determine the thermal death point against natural 
difficulties, so that the results might be applied with confidence to 
practical pasteurization. 
BACILLUS TUBERCULOSIS. 
Certain special difficulties are met with in determining the thermal 
death point of the tubercle bacillus. This organism does not grow 
readily upon artificial media. The few experiments made to deter- 
mine its thermal death point by cultural methods have no signifi- 
cance, because its vegetability upon artificial media does not corre- 
spond to its power of growing in the animal organism. It is therefore 
necessary to inoculate animals in order to determine whether or not 
the tubercle bacillus is alive and virulent. Here again we meet with 
complications. Dead tubercle bacilli have a certain amount of 
pathogenic power and produce lesions, including tubercle formation, 
abcesses, and coagulation necrosis. However, while we lack a cri- 
terion to determine with precision the exact point when the tubercle 
bacillus dies, we are able by means of animal inoculations to deter- 
mine just when the tubercle bacillus is so enfeebled that it is no 
longer able to infect. This, after all, is the important practical point. 
ORIGINAL EXPERIMENTS. 
In all the tubercle experiments raw whole milk was used, the chem- 
ical composition of which is stated in each case. The number of 
bacteria other than the tubercle bacillus was determined by the usual 
method on agar plates. 
The young tubercle cultures were rubbed up with the milk in a 
mortar until a fairly uniform suspension was obtained. Otherwdse 
the methods used were those given on page 9. 
Nine experiments were made with five different bovine cultures, 
the details of which will be found in the following tables. The results 
are consistent so far as the thermal death point is concerned. The 
only irregularity will be found in Table No. 1, guinea pig No. A12. 
This animal did not have lesions differing markedly from those caused 
by dead tubercle bacilli; but the secondary guinea pig (Al2^) died 
as a result of generalized tuberculosis, affecting especially the lungs. 
The secondary guinea pig, inoculated with the lesions of A9, remained 
well. The other animals of this series, namely, A7, A8, AlO, and All, 
evidently did not have an active tuberculosis due to living and viru- 
lent tubercle bacilli. 
