n6 



THE MICROSCOPE. 



Pasteur. The culture liquid is introduced into these through 

 suction, then the slender extremity is closed by melting it in a lamp, 

 and finally the liquid is sterilized by heat. In order to make sure 

 that no atmospheric germ has got into the bulbs while being filled, 

 the latter are tested by allowing them to remain for a month in a 

 stove at a temperature of 3o°-35". If they do not become turbid, 

 they are considered as adapted for the sowing. This latter is 

 effected in different ways. If it concerns rain water, the latter is 

 collected in the collector, P., of a rain gauge (Fig. 8.) This col- 





1 



figs. 6 and 7. 



lector is carried by a movable arm, so that the operator placed at a 

 distance can take it and put it very gently under the funnel, E, of 

 the apparatus. 



Mr. Miquel has applied this arrangement to the estimation of 

 the number of bacteria contained in rain-water, and has thus ascer- 

 tained that at the beginning of storms such water contains fifty of 

 these organisms to the cubic centimeter, and that this number soon 

 begins to diminish, although it increases again at times at the end 

 of a few days of damp and rainy weather. It seems then, that 

 bacteria are capable of multiplying in the clouds, or that the latter 

 become charged with them mechanically during their travel through 

 space. At Montsouris, out of 100 bacteria contained in a drop of 

 rain-water, there were, on an average, 28 Micrococci, 63 Bacilli, and 



