200 BACTERIA. 



unless Ihey are very well supplied with both air and light, 

 whilst on the other hand such organisms as usually grow in 

 the body appear to become markedly weaker as regards their 

 power of growing and of giving rise to their special dele- 

 terious products if they are freely- exposed to the light. 

 Recently Dr. Janowski has made a nurnber of experiments 

 by exposing growths of the typhoid bacillus to the action of 

 light, and has found that it exerts a distinctly depressing 

 action on the typhoid organism, an action entirely inde- 

 pendent of any oxidation of the food material that might 

 occur under the action of the chemical rays, these chemical 

 rays acting directly upon the protoplasm and rendering it 

 incapable not only of further development but of continuing 

 alive. In order to prove his thesis he took a gelatine tube 

 in which typhoid bacilli had been sown and exposed it to the 

 action of the light on a cold winter day ; a similar tube 

 inoculated with the same bacillus was wrapped up in a layer 

 of black paper and then in one of white paper, this also 

 was exposed in the same position. The light in this case 

 delayed the development and the multiplication of the 

 organism in a somewhat marked manner, as in the two pro- 

 tected from the light, growth took place in three days, whilst 

 in that exposed to the light, it did not commence for five 

 days. Of course the growth here referred to is measured by 

 the size of the colony that can be seen with the naked eye 

 and although both were probably growing during the whole 

 time, the rate of multiplication in the one was very consider- 

 ably greater than in the other. In order that there might be 

 no doubt as to the identity of the organism and the quantity 

 sown in each tube, a U-shaped tube (a double Pasteur tube) 

 was taken and the inoculation was made ; the fluid was 

 thoroughly mixed by passing from one limb of the tube to 

 the other, then one limb was protected as above and the 

 other was exposed to the light ; similar results were obtained, 

 the bacilli in the limb that was exposed to the light being 

 considerably delayed in their development. He fdund that 

 direct sunlight acting on fluid cultures of the typhoid bacillus 

 kills the organisms in the short space of from four to seven 

 hours, but diffused light requires a considerably longer period 

 to entirely arrest the development and multiplication of the 

 organisms. Instead of analysing the rays of light by means 

 of a prism, as Englemann and others had done, Janowski 



