TILE MULTIPLICATION OF MICROORGANISMS 221 



this temperature brought about a marked decline, whilst 

 subsequently again a slight increase was observed. 



These figures are intelligible if we remember, in the 

 first place, the large quantity of bacteria present in this 

 raw river-water ; secondly, the numerous different 

 varieties which invariably are found in such descriptions 

 of water. These different varieties have each an indi- 

 viduality of their own, and whilst some flourish luxuri- 

 antly at a high temperature, others are destroyed by it. 

 Thus we find in the first twenty-four hours an enormous 

 increase in those forms which the heat of the incubator 

 has placed at the greatest advantage. In the course of 

 this multiplication they may have, and doubtless have, 

 elaborated products which act ultimately inimically 

 upon themselves, so that the field is cleared for the 

 subsequent development and multiplication of those 

 forms which had previously remained dormant. 



As regards the effect of a rise of temperature upon 

 the bacteria in water, Kr tiger 1 has more recently (1889) 

 found that in samples of water examined by him at 

 Jena, and kept for twenty hours at 7 C., the numbers 

 present increased 0'08 times, at 10 C. 4'8, and at 12 C. 

 5'3 times ; it must not, however, be supposed that these 

 factors are capable of any general application, but they 

 serve to indicate in a concise form the multiplication 

 phenomena which took place in a particular instance. 



Experiments were then instituted to compare the 

 powers of multiplication possessed by the bacteria in 

 the raw river-water with those remaining in the same 

 water after undergoing storage and filtration at the 

 hands of the water companies. 



For this purpose, samples were collected from the 

 mains of the various companies and subsequently ex- 



1 Zeitsclirift fur Hygiene, vol. vii. p. 90. 



