Report on the Bacteriology of Water. 



315 



remained in the water it would have multiplied abundantly ; but the 

 waters, even after this treatment, proved innocuous to animals 

 (pp. 209—212). 



12. The striking results obtained by direct insolation at low tem- 

 peratures in the open air in winter bring vividly before us the 

 extreme importance of this bactericidal action of direct sunlight, for 

 they show conclusively that the action is direct, and not due to any 

 rise of temperature from the heat rays (pp. 303 — 310). Other facts 

 and their consequences are given in the conclusions to Part II. 



13. We found that when the spores were introduced even in very 

 large numbers into unsterilised waters in their natural condition, they 

 were often no longer recognisable by the ordinary cultivation methods 

 after the lapse of a few days, and it was only by resorting to special 

 methods of detection that the anthrax spores could be discovered. By 

 employing these special methods, however, we have conclusively 

 shown that the number of anthrax spores undergoes a continuous 

 decline in such unsterilised waters, and thus presents a marked con- 

 trast to the persistence of the numbers in the sterile waters referred 

 to above. Notwithstanding this decline in the number of anthrax 

 spores, their presence could still be demonstrated many months after 

 their introduction into the Thames water, and this infected water 

 still retained its power of killing animals after upwards of seven 

 months (pp. 278 — 283), either by direct inoculation (when large num- 

 bers of anthrax spores had been originally introduced) or after pre- 

 liminary incubation with sterile broth (which had to be resorted to 

 when only a small number of anthrax spores was originally intro- 

 duced, pp. 192—200, 214—219, 229—231, 236—238). 



In the case of the Thames water we found but little difference in 

 the result when the waters were kept at winter and summer tempera- 

 tures respectively, but in the case of the Loch Katrine water a 

 marked difference was exhibited in this respect, for at the summer 

 temperature (18 — 20° C.) the anthrax spores underwent such rapid 

 degeneration that after three months they were no longer recognis- 

 able by cultivation. Moreover, the water kept at the summer tem- 

 perature proved in every case to be no longer fatal to animals when 

 inoculated directly, and out of two such specimens of water which 

 had been specially incubated with broth for the purpose of revivifying 

 any lurking anthrax spores that might remain, only one became viru- 

 lent, showing that in the other at least complete extinction of the 

 anthrax spores had taken place. It is suggested that this compara- 

 tively rapid destruction of the anthrax spores in unsterilised Loch 

 Katrine water at 18 — 20° C. is due to the elaboration of bactericidal 

 products by the water bacteria, and not to the character of the moor- 

 land water itself, for in the sterile Loch Katrine water the destruction 

 of anthrax spores at this temperature did not take place (pp. 228 — 239). 



