76 BACTERIA IN DAILY LIFE 



the numbers remained practically unchanged. 

 Professor Buchner, of Munich, demonstrated the 

 same impotence of the sun's rays to destroy 

 bacteria much beneath the surface of water, in 

 some ingenious experiments he made in the 

 Starnberger See, near Munich. He lowered glass 

 dishes containing jelly thickly sown with typhoid 

 bacilli to different depths in the water during 

 bright sunshine ; those kept at a depth of about 

 five feet subsequently showed no sign of life, 

 whilst those immersed about ten feet developed 

 abundant growths ; in both cases the exposure 

 was prolonged over four and a half hours. 



In our own rivers Thames and Lea frequently 

 about twenty times more microbes have been 

 found in the winter than in the summer months, 

 but it would be extremely rash to therefore infer 

 that the comparative poverty of bacterial life was 

 due to the greater potency of the 'sun's rays in 

 the summer than in the winter. Doubtless it 

 may contribute to this beneficial result ; but we 

 know as a matter of fact that, in the summer, 

 these rivers receive a large proportion of spring 

 water, which is comparatively poor in microbes, 

 and that this factor also must not be ignored in 

 discussing the improved bacterial quality of these 

 waters at this season of the year. 



Another point which must be taken into con- 



