MECHANISM OF DEATH 



271 



broth, the other in the same broth + 3% glucose + 5% horse serum. 

 The results (Table 75) show that, according to the standard broth 

 test, the spores of strain SM were apparently killed between four 

 and six minutes, and of strain Og between ten and twelve minutes of 

 heating. However, the test in the better medium proved that 

 this conclusion was wrong, as some of the spores revived and ger- 

 minated after twenty-five minutes of heating in the richer medium. 

 The destruction of the spores by heat was the same in both SM and 

 Og cases because the tests were made with duplicate samples. Life 

 in the spores was suspended irreparably in standard broth after 

 four to twelve minutes of heating, while in the better medium, 

 some of these spores recovered, and the fatal stage was not reached 

 until they were heated for about thirty minutes. 



Table 75. — Viability of Spores of B. anthracis, after Heating in 



Steam 

 (+ means growth; means no growth; — means not tested) 



From this experience, it may well be postulated that with a still 

 better test medium, it might be proved that even forty minutes is 

 not sufficient to really kill all spores. Similar experiments have 

 been recorded in Hterature. 



Death, as defined above, is, therefore, a function of the test 

 medium. It might be recalled here that in the earlier development 

 of agricultural bacteriology, much time was spent on finding the 

 best medium which would give the highest plate count in milk, or 

 in soil. Since the numbers of colonies developing from the same 

 sample on different media are quite different, some cells are counted 

 as "living" on one medium while they are ''dead" on the other. 



