QUANTITATIVE BACTERIOLOGICAL ANALYSIS. 17 



anthrax spores. They found that the sun's rays in December 

 killed the spores in gelatine plates after a few hours exposure, 

 although the temperature was so low that the plates were not 

 liquefied. The spores also seemed to be more resistant to the 

 action of sunshine when diffused in water than when sown in 

 ordinary culture materials. Ward showed that the spores were 

 killed by the direct action of sunlight and not through changes 

 in the media. 



The following conclusions seem to be justified by the results 

 obtained up to the present time: 



(1) There is no doubt that light, and especially sunlight, has 

 an injurious action on micro-organisms, and that it acts directly 

 on bacteria as well as by producing changes in the culture 

 media. 



(2) The action of light is greatly increased by the presence of 

 air and moisture, the process being largely an oxidation attended 

 by the development of hydrogen peroxide. 



(3) The precise duration of exposure required to destroy 

 micro-organisms must necessarily vary with the intensity of the 

 light and the inherent vitality of the various species. 



(4) The influence of sunlight probably extends through water 

 to a distance of about two metres, but undue reliance must not 

 be placed on its bactericidal powers even in shallow streams, as 

 the micro-organisms may be attached to suspended particles, and 

 so protected to a great extent from the action of light. 



THE INFLUENCE OF MOVEMENT AND REST ON MICRO- 

 ORGANISMS. 



Cramer investigated the action of movement by shaking a 

 specimen of water for four hours. He found 80 bacteria per c.c. 

 in the water which had been standing for the same time with- 

 out shaking, and 87 bacteria per c.c. in the water which had 

 been shaken. 



Leone found no difference in the number of bacteria in a water 

 before and after shaking. 



Miquel obtained similar results when working with the water 

 from the Varne and Dhuis. Tiemann and Gartner found such 

 slight differences that shaking was considered to have very little 

 influence. Schmidt could not find any difference in the growth 



