560 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Dry Mounting of Opaque Objects.* — lu tho cftsc of opaqiio 

 objects it frc(iiiciitly happens that the cover-ghisa becomes covered 

 with a fihn of oily or watery particles which cuucleusc upon its under 

 surface. Prof. W. A. Rogers, whose rulings, as formerly prepared, 

 were freqiiently injured in apjiearancc by this condensation, has at 

 last, so he believes, entirely obviated this annoj'ancc. Ho now uses 

 a brass ring for a cell to hold the ruled cover-glasses, but free 

 communication between the air within and without the cell is estab- 

 lished through a minute perforation in the side of the cell. Some 

 preparers have been in the habit of maintaining this free communica- 

 tion by leaving a bristle or a thread passing through the wall of tho 

 cell until the mount is finished, after which it is withdi'awn, thus 

 making a minute perforation. 



Examination of Water for the Development of Micro-organisms.f 

 — The following methods arc recommended by Dr. Tiemanu. 



200cc. of water are placed in vessels carefully purified, disinfected 

 by hot air, and plugged with disinfected cotton wool. The water is 

 drawn up by a pipette, which has been well washed with distilled water. 

 A drop of the Avatcr, which has been well shaken, is placed on a cover- 

 glass, which is set with the droj) downwards on a glass slide 

 hollowed out in the centre, and magnified 100-500 times. Several 

 such preparations are allowed to dry on the cover-glass, and then 

 stained with methyl-blue, dried, and mounted in Canada balsam. The 

 bacteria are thus stained blue. 



To estimate the numbers of the organisms in the water, a certain 

 quantity (1/1000-10 drops) is mixed with nutrient jelly. The quan- 

 tity is measured in a graduated pipette, which has been previously 

 heated, and washed with distilled water as well as several times with 

 the water under examination. Each sample is added to 10 cc. of lique- 

 fied jelly, which is spread on a glass plate previously sterilized by 

 heat. The colonies develop in the jelly, beneath a bell-jar, the air in 

 which is kept damp, at various parts of the plate, and the number per 

 square cm. is counted under a magnification of 30 diameters. The 

 mean of the values thus obtained x the area of the jelly gives the 

 number of organisms in the sample, and the number of tlie same 

 per cc. of water can be calculated. For counting, one uses a plate 

 divided into square centimetres, which is placed beneath the test- 

 plate. Tho estimated is always less than the real number, as some 

 colonies cover each other, and all the micro-organisms do not 

 developc. 



Examination of Water for Organisms. :|: — If a sample of water 

 contains but few organisms, these may easily escape observation under 

 the Microscope. Mr. H. S. Carpenter and Mr. W. O. Nicholson have, 

 therefore, devised a method by which these organisms may be culti- 

 vated, and consequently become so numerous as to bo readily recog- 

 nizable. 



* Amcr. Mou. Micr. Journ., v. (1884) pp. 210-11. 

 t Verli. Dcutsch. Gesell. i. uftentl. Gcsundbeitspflese zu Berlin, 1883. 

 X Anal^-st, ix, (1885) pp. 04-6. See Jouru. Chem. Soc. — Abstr., xlviii. 

 (1885) pp. 442-3. 



