[shanly] heat resistance OF BACTERIAL SPORES 125 



while that in the inner could not be raised above 94° or 95 °C. This 

 great loss of heat is obviated by covering the various compartments of 

 the water-bath. By this means we were eventually able to bring the 

 temperature of our different compartments to within a degree of differ- 

 ence within five to ten minutes. 



3. It seemed to us — although here we may be introducing un- 

 necessary refinement — that the temperature in our control test tube 

 could be preserved at a more even level if, instead of the ordinary two 

 compartments, we suspended in the ordinary large water-bath (about 

 a foot across, outside measurement) a beaker filled with water to con- 

 tain the tubes which were being tested. This method, it is true, by 

 bringing the surface exposed during the various manipulations to a 

 minimum, reduced the amount of evaporation and loss of heat. In this 

 way we found that we could without difficulty keep the contents of 

 our test-tubes for sixty minutes at a temperature which with occasional 

 and by no means constant oversight varies within but two degrees 

 during the experiment. 



4. In his observations upon the thermal death point of tubercle 

 bacilli present in milk, Theobald Smith ^ has explained the occasional 

 survival of tubercle bacilli after an exposure as long as sixty-five 

 minutes to a temperature of 60°C. (whereas in bouillon and distilled 

 water at most fifteen to twenty minutes is necessary to kill all bacilli 

 at this temperature) by the formation of a surface pellicle over milk 

 heated in the air. In this, he states, the bacilli are carried by fat 

 globules which shield them from the effects of the heat. Our observa- 

 tions suggest to us that here Theobald Smith has not afforded the 

 whole explanation. It is not the mere formation of the pellicle that 

 preserves the bacilli, but in addition this pellicle is the site of evapora- 

 tion and cooling so that its temperature in consequence of evaporation 

 is distinctly lower than that of the mass of underlying fluid. Milk 

 suspensions of the bacilli in sealed pipettes were killed in the usual 

 time. As has been pointed out, this surface evaporation and rapid 

 loss of heat is easily prevented in the water-bath by closing the various 

 compartments above. It has seemed to us that a similar arrest of 

 evaporation and so of surface cooling is to be obtained by lightly plug- 

 ging the test-tubes with cotton wool. To make quite sure, however, 

 that our results or some of them, have not been due to this cooling of 

 the surface film, we have made tests in which four test-tubes containing 

 an equal amount of Anthrax spores have been placed for sixty minutes 

 in the water-bath at a temperature of 85 °C. Two of the test-tubes 

 had poured into them a covering layer of albolene, the other two being 



1 Jour. Exper. Med., Vol. IV., 1899, p. 217. 



