38 MORPHOLOGIC VARIATION 



that the inhibition of growth was due to a non-filterable thermolabile 

 substance. Unlike Eijkman, however, he found that the organisms 

 could be killed with ether (subsequently evaporated off) without 

 destroying the inhibitory effect. A heated forty-eight-hour culture, 

 re-inoculated, gave a good growth; a similar culture treated with 

 ether gave no growth, but when heated later again allowed growth 

 to occur; a tube of sterile broth treated with ether as above gave 

 a good growth, showing that the ether treatment itself was not 

 inhibitory; the same was true when a heated forty-eight-hour culture 

 was treated with ether. Here is a clean-cut experiment which would 

 seem to allow but one conclusion, namely that some substance inhibi- 

 tory to growth had been formed, which was destroyed by heat but 

 not by ether. The failure to pass a porcelain filter was explained 

 by its adsorbability ; small pieces of a filter placed in an ether-treated 

 tube served to destroy the inhibiting effect. A number of other 

 organisms were tried, but most of them could not be killed by the 

 ether treatment; only three others, B. lactis erythro genes, Vibrio lac- 

 tis, and Micrococci's grossus, gave positive results. One might sus- 

 pect that here we are dealing with a special case not generally 

 applicable to bacteria at large, that perhaps the substance is pyocya- 

 nase or a related substance. 



Chesney observed that curves of death of pneumococci in cultures 

 appeared to follow the monomolecular law, as had previously been 

 shown to be the case when bacteria are killed by disinfectants; and 

 that when pneumococci are centrifuged out of an actively growing 

 culture the remaining cells continue to grow actively, but if the 

 culture be centrifuged after the period of maximum growth the re- 

 maining cells in the supernatant liquid show a prolonged lag and 

 may even die for a time. Culture filtrates from twenty-four-hour 

 cultures tended to inhibit the growth of actively growing pneumo- 

 cocci inoculated into them, the inhibitory action being lost if the 

 filtrates were held for a time at incubator temperature. Actively 

 growing pneumococci exposed to the action of a twenty-four-hour 

 culture filtrate at low temperature showed a longer lag than controls. 

 Filtrates of four-day-old cultures failed to inhibit. He concludes 

 that the inhibition of growth is due to some unstable toxic product 

 of growth which injures the cells. M'Leod and Govenlock also be- 



