Report on the Bacteriology of Water. 



311 



who have attended to the question, we find these water bacteria to 

 multiply with astounding rapidity if the water is allowed to stand for 

 a few days ; the maximum numbers are reached in from one to four 

 days as a rule, and the curve itself is exceedingly steep and sharp 

 (pp. 249—256). 



5. Our observations go to show that the rapidity of increase and 

 the maximum numbers reached depend on various factors — tempera- 

 ture, oxygen supply, the amount and quality of the food materials in 

 the water, and the nature and numbers of the bacteria concerned 

 (pp. 254, 291, 295, 299—302). 



6. We have experimented with the waters, chiefly of the Thames, 

 in three conditions, viz. : — (1) fresh from the river and not subjected 

 to any treatment ; (2) deprived of all of the above bacteria by 

 filtration through porous porcelain; and (3) sterilised by heat. 

 (4) Experiments have also been made with distilled water. We 

 regard the four conditions of water referred to as essentially different' 

 one from another (pp. 259—263, 266—273, 275—278). 



7. We have employed such waters to test the power of resistance of 

 Bacillus anthracis (anthrax) both in the form of spores and of vege- 

 tative bacilli, and also in the asporogenous state (pp. 256 — 285). 



8. We have, moreover, employed the anthrax in a virulent and in 

 a weakened condition (pp. 266 — 273). 



9. And we have experimented under various conditions as regards 

 (1) time, (2) temperature, (3) light, (4) the presence of other organ- 

 isms, with the following results briefly summarised : — 



10. Neither as spores nor as bacilli — weak or strong — is anthrax 

 killed forthwith in any of the waters under any of the conditions 

 tested ; but the spores are immensely more resistant than the 

 bacilli (pp. 259—285). 



11. In the dark, and at moderate temperatures, the spores of 

 anthrax retain their powers of germination and infection for many 

 months — we have proved up to eight months — in any of the waters 

 referred to (pp. 278— 283). 



12. In direct sunlight, however, the spores in the waters undergo 

 rapid destruction, depending on the intensity of the insolation and 

 the time of exposure (pp. 279, 283, 303). 



13. That this destruction is directly due to the light-rays, espe- 

 cially at the blue end of the spectrum, and not to a rise oi temper- 

 ature fatal to the spores, is definitely proved by the experiments 

 with gelatine and agar plates. These experiments also demonstrate 

 conclusively that the bactericidal action is really direct, and not due 

 indirectly to the action of the solar rays on the medium (p. 310). 



14. The value of the experiments on the bactericidal action of 

 direct sunlight on the spores of B. anthracis is the more important 

 when it is reflected that the most decisive results have been obtained 



