166 MICEOBES, FEKMENTS, AND MOULDS. 



These numbers are the minima. The putrefaction 

 of stagnant sewer-water produces germs from which, 

 in a few days, microbes are multiplied by thousands. 



Certes, in France, and Maggi, in Italy, have lately 

 been occupied with the micrographic study of drink- 

 ing-water. These observers reveal the presence of 

 microbes in the water under examination by means 

 of staining reagents. The reagent most in use is a 

 1'5 per cent, solution of osmic acid (Certes). Osmic 

 acid kills the microbes without changing their form, 

 and precipitates them to the bottom of the glass 

 vessel, whence it is easy to collect them. A cubic 

 centimetre of the solution suffices for 30 or 40 cubic 

 centimetres of water. It is allowed to settle, then 

 the liquid is poured off, and the thick, dark-coloured 

 deposit which remains consists of aU the organisms 

 previously diffused in the liquid, and may be examined 

 under the microscope. The only drawback to the 

 use of this reagent is the high price of osmic acid, 

 a matter worth consideration in the extensive and 

 comparative researches necessary in these cases. 

 Maggi obtained analogous results with chloride of 

 palladium, and Certes with iodide of glycerine, and 

 alcoholic solutions of cyanine, gentian, etc. ; but none 

 of these reagents are as efficient as osmic aicid, of 

 which the effect is more precise, constant, and durable. 



Microbes of the Soil. — The presence of microbes in 

 the soil has been proved by Pasteur and his feUow- 

 workers, Chamberland and Roux, in the researches into 



