THE MULTIPLICATION OF MICRO-ORGANISMS 229 



rate those which are non-volatile, can be obtained in a 

 concentrated form by evaporating a large volume (eight 

 to ten litres) of the water containing them at a low 

 temperature (30 to 35 C.); the concentrated solution 

 which remains is then found to be actually toxic to 

 some animals, and when introduced into waters pre- 

 vents bacterial multiplication taking place in the latter. 



It is very satisfactory to find independent experi- 

 mental confirmation of some of these interesting and 

 highly suggestive observations of Miquel's in the work 

 of the Massachusetts State Board of Health. In the 

 Eeport 1 of the latter, to which we have already referred, 

 experiments are recorded in which the power of multi- 

 plication of water bacteria is contrasted in one and the 

 same water before and after boiling. Thus a quart of 

 water from the City Service pipe was boiled in a clean 

 flask with a return condenser for one hour and so ren- 

 dered sterile. After cooling, it was mixed with 10 per 

 cent, of unboiled city water. A control flask was filled 

 with the same water unboiled, and both flasks, covered 

 merely with inverted sterile beakers, were kept' at the 

 same temperature. 



The following are the results obtained : 



Boiled Water infected with Water Microbes 

 (Massachusetts Report) 



Number of bacteria in 1 c.c. 

 Date 



City water unboiled City water hoiled 



May 14, 1890 

 17 

 21 



27 



June 4 

 7 



10 

 13 



196 3 



79 74,880 



31 162 864 



759 90,000 



12 103,486 



63,140 



128,040 



530 



1 Report for 1890, p. 593. 



