THE MULTIPLICATION OF MICRO-ORGANISMS 247 



this author remarks that the strength of the solution 

 must be carefully watched, as in samples which are no 

 longer fresh it becomes diminished, and consequently 

 -does not act so effectually. 



The authors do not, however, appear to have taken 

 notice of the fact that ordinary commercial samples of 

 peroxide of hydrogen usually contain free sulphuric 

 acid, the quantity of which may have materially affected 

 the results obtained. 



These results are also of interest in connection 

 with the possible cause of the bactericidal action of 

 light (see p. 389). 



Influence of agitation on the multiplication of bacteria. 

 A number of experiments have been conducted in 

 order to ascertain whether the remarkable multiplica- 

 tion of water bacteria to which we have devoted this 

 chapter is in any way influenced by the circumstance 

 of the water being at rest or in violent motion. 



Notwithstanding the apparent simplicity of this in- 

 vestigation, the effect of agitation on the multiplication 

 of bacteria suspended in water is still a matter of dis- 

 pute, the results in the several experiments made being 

 very contradictory. Poehl, 1 in a paper published in 

 1884, describes some investigations made by him on 

 this subject. Bottles of water were attached to a cen- 

 trifugal machine, and after one hour's agitation samples 

 were submitted to plate-cultivation, and the results com- 

 pared with those obtained from the same water before 

 agitation. The most astonishing results were recorded, 

 for it was found that a water containing originally 4,147 

 microbes per c.c., after being simply violently shaken 

 with the handfor one hour, contained 728, whilst after the 

 centrifugal agitation for the same length of time only 533 



1 Chemische und Bakteriologische Untersuchungen betreffend die 

 Wasserversorgung St. Petersburgs, Petersburg, 1884, p. 24. 



