360 MICRO-ORGANISMS^lN WATER 



Kotljar found, however, that the red rays appeared to 

 favour the development of the micro-organisms, whilst 

 the violet rays hindered their growth. This observer 

 made by chance the interesting discovery that the 

 violet rays, however, actually favoured the sporulation 

 of the B. pseudo-anthracis. 



We will next consider, for the sake of continuity, 

 some experiments made by Buchner ^ on the action of 

 light on the typhoid bacillus, although a memoir by 

 Momont on the behaviour of anthrax bacilli during in- 

 solation comes first in chronological order of publica- 

 tion. The first paper by Buchner contains an account 

 of some experiments on the effect of insolation on 

 bacteria in water. As we shall take those investi- 

 gations which deal especially with water separately 

 into consideration, we will pass on to his second com- 

 munication, in which nutritive agar-agar was employed 

 as the culture medium. For this purpose agar-agar 

 contained in test-tubes was rendered fluid, and then 

 inoculated with pure cultivations of various bacteria 

 and poured into Petri dishes. When the contents had 

 solidified, a piece of black paper with letters of the 

 alphabet cut out was fastened on to the under- side of 

 the dish by means of an india-rubber band, and the dish 

 was then exposed bottom upwards to direct sunlight 

 for from one to one and a half hour, or during five 

 hours to diffused light. After this exposure the dishes 

 were incubated in a dark place. Already in twenty- 

 four hours' time the letters of the alphabet employed 

 appeared sharply defined on the culture material, for 

 where the black paper screen had protected the bac- 

 teria underneath from the action of the sun's rays there 



^ ' Ueber den Einfluss des LichteB auf Bakterien ' (No. 1), Central- 

 hlatt fiir BaMeriologie, vol. si., 1892, p. 781. Ibid. (No. 2), loc. cit 

 vol. xii., 1892, p. 217. 



