EXAMINATION OF WATER. 745 



matter. A tall white glass vessel, holding a gallon at 

 least, must be filled and allowed to stand by forty-eight 

 hours. When all the sediment is settled down, the 

 water must be siphoned off, with the exception of just 

 a sufficient quantity to permit of the residual sediment 

 being shaken up and poured out into a conical glass. 

 After standing a short time, small portions of the sedi- 

 ment may be dipped out with a pipette, dropped on to 

 a glass-slide, and covered over with a thin glass cover. 

 The thin glass cover tends to equalize refraction and 

 spread the drop evenly out before it is placed under 

 the microscope. 



M. Certes, when dealing with small quantities of 

 organic matter taken from water, and having only a 

 very minute amount of sediment, employs osmic acid. 

 This re-agent kills all animal life and blackens it ; it 

 is then more readily seen. A single drop of a half per 

 cent, solution of osmic acid is quite sufficient. If used 

 stronger it produces, by reason of its too rapid action, a 

 (shrivelling or charring of the organisms. For the better 

 detection of bacteria and other minute bodies, dissolve 

 ten grains of pure white sugar in ten ounces of the sus- 

 pected water in a tall white glass measure, cover it over 

 with muslin and let it stand exposed to light for forty, 

 eight hours. If sewage be present the water will become 

 turbid and a thin scum of bacteria form on the top. 



Banvier recommends the use of picro-carmine solu- 

 tions, with glycerine for staining and colouring the 

 living organisms in the water, and by means of which 

 they are more easily detected. In this way the very 

 minutest forms of life bacteria, amoebiform particles 

 of protoplasm, the delicate flagellae, and the locomotive 

 organs of Monads, will become visible under a high- 

 angled one-eighth objective. 



The sanitary import of such organisms as bacteria, 

 their probable danger to health and life, their per- 

 sistency and great power of multiplication, all tend to. 

 render them objects of deep interest to the physiologist 

 and the medical practitioner. Bacteria have been long 

 known to microscopists ; their active vibratory motion 

 have attracted the attention of every observer. From 



