622 Journal of Applied Microscopy. 



rubber tube, measuring six inches long by three-sixteenth inch diameter, is 

 cemented into it. A piece of glass tubing (B) one inch in length is closed at one end ; 

 and a small hole is bored through it at about a quarter of an inch from the 



closed end. The open end 

 of the glass tube is then 

 slipped into the free end of 

 the rubber tube, and the two so 

 arranged that the hole in the 

 former shall be just covered 

 by the India rubber. To use the apparatus, place the mount containing the air 

 bubbles in the wooden cell, and cover it over with a second slip of glass measur- 

 ing 4" X 1 ^2 ", the edges of which have been previously greased with tallow. If the 

 frame has been accurately made the cell will now be airtight. Exhaust the cell by 

 drawing the air through the tube. The valve formed by the hole will prevent 

 the re-entrance of air, and any bubbles contained in the mount will quickly 

 disappear. J. H. Cooke. 



London, Eng. 



On the Bacteriological Tests Applied to the Effluent of the 

 South Norwood Irrigation Farm.— Prior to 1894, it had not occurred to the 

 authorities in charge of the sewage farm at South Norwood, London, to utilize 

 the microscope in their examinations of the effluents from the farm. In that 

 year, however, Dr. J. M. Hobson, M. D., B. Sc, undertook to supplement the 

 usual weekly chemical tests with periodical bacteriological examinations, and 

 these were attended with such interesting and valuable results that they have 

 been conducted regularly, at fixed intervals, down to the present time. His 

 microscopical investigations may be broadly divided into two separate pro- 

 cesses. The first is an enumeration of the organisms in measured quantities of 

 screened sewage and of effluent respectively ; the second is an isolation of spec- 

 ific organisms in the screened sewage and the effluent. The following is a brief 

 outline of the processes and methods that he adopts in his work. 



To enumerate the organisms, a sample is conveyed to the laboratory as soon 

 as possible, and surrounded with ice. A measured quantity is taken and diluted 

 with a measured quantity of sterilized distilled water. This is thoroughly mixed, 

 and a measured quantity of the diluted matter is added to a tube of melted, 

 sterilized nutrient gelatin. This is thoroughly mixed by oscillation and the 

 whole mass is poured out on a Petri plate, and instantly covered up. 



When the gelatin has set, the plate is placed in an incubator and kept 

 there at the constant temperature of 20° C. for two or three days, for colonies 

 to form. 



These colonies appear as little beads in the transparent gelatin. By gen- 

 eral agreement each colony counts as one organism, i. e., an organic unit without 

 any reference to specific identity. The counting then begins. A black card, 

 ruled off into small squares of equal area, is placed beneath the plate of colonies ; 

 these squares are numbered. The number of colonies in a given square is 

 counted with a low magnifier, and the number is noted on a correspondingly 



