126 THE ROYAL SOCIETY OF CANADA 



employed as controls. At the conclusion of the heating, agar plates 

 were made from each of the four tubes. These results were as follows: 



The test was repeated three times, each time with greater accur- 

 acy, and each time, strange as it may seem, the average number of 

 colonies on the plates from the broths protected by albolene was greater 

 than that of the other plates. Clearly the protective effects of a sur- 

 face tension layer has been overcome.^ 



As the result of these various preliminary tests, we employed for 

 these observations the water-bath represented in the accompanying 

 diagram. The compartments A and B represent the compartments of 

 the ordinary water-bath, C. represents a glass beaker 4 inches in diam- 

 eter, fitting into and suspended by a circular opening in the copper disc 

 D made of 0.1 inch copper. Covering C is another disc, E, of the 

 same metal provided with a dozen openings, each nine-sixteenth of an 

 inch in diameter, permitting thus the passage through them of test- 

 tubes to half an inch in diameter. The test-tubes, it will be seen, are 

 immersed so that the level of the contained fluid is well below the level 

 of the water and that the air is also heated. 



Since elaborating this apparatus we have found that Rosenau^ 

 has employed a very similar apparatus. He likewise has closed in the 

 upper surface of his water-bath, and has determined the thermal death 

 point by placing the thermometer within the test-tubes in which are 

 the suspensions. On the other hand he employed two, not three 

 compartments, and says nothing about closing the test-tubes so as to 

 reduce evaporation and surface cooling. 



What is quite the most accurate and delicate instrument yet 

 devised for testing the heat resistance of spores is the apparatus of 

 C. Balfour Stewart,^ in which the outer jacket contains benzol boiling 

 at 80°C., the inner closed chamber, whether it contains air or water, 

 if worked properly can thus maintain a constant temperature of 80°C. 

 This instrument is admirably adapted for testing the resistance of 

 spores to what may be termed the critical temperature of 80°C. over 

 periods of different length — five minutes, ten minutes, an hour, etc. 

 For this research in which it is desired to determine the resistance of 

 endospores subjected for a constant time to different temperature^ 

 the apparatus cannot be employed. 



A point in our procedure that is sure to be criticised is the employ- 

 ment of peptone broth for our suspensions rather than distilled water. 

 It is generally accepted that the thermal death point of bacteria varies 



^A possible explanation of this result is that given by Theobald Smith, namely 

 that oily matter in the fluid formed a protective layer about those spores which came, 

 into immediate contact with the layer of albolene. 



2 U.S. Treasury Dept., Hygiene Lab. Bulletin No. 42, Jan. 1908. 



3 Thompson Yates Laboratory Reports, Vol. HI, Pt. I, 1900, p. 38. 



