94 SOLID CULTIVATION MEDIA. 



either by heat, or a solution of perchloride of mercury one-tenth per 

 cent, (see Fig. 48). At one corner of the plate is placed a small spirit 

 level, by the aid of which, and the screws on the feet, the frame is 

 ' adjusted until the plate is perfectly level. 



A number of smaller glass plates (of such a size that they will 

 readily go under the bell jar) are then put into a sheet-iron box, with 

 an overlapping lid, and are exposed to a temperature of 170° C. for 

 at least one hour in the hot air chamber. They are then allowed to 

 cool, and, after the operator's hands have been perfectly purified by 

 means of soap and water and perchloride of mercury solution, one of 

 the plates is taken out and rapidly transferred to the tripod on to the 

 larger plate and under the bell jar. A small quantity of the pepton- 

 ised meat jelly, about 5 c.c, in a sterilised test-tube is warmed in a 

 water bath until it is quite fluid, and then a couple of drops or more 

 of the water to be examined are carefully introduced by means of a 

 fine pipette. (The drops of water must all be of equal size.) The 

 sterile plug of wadding is rapidly returned to the mouth of the test- 

 tilbe. The whole mass, whilst still warm, is well shaken; then, raising 

 the bell jar carefully, the liquid is poured out on to the small glass plate, 

 and the bell jar is lowered. The measured squares on the larger plate 

 are easily seen through bell jar, upper plate, and layer of gelatine ; but, 

 for the sake of convenience, the upper plate may be ruled, especially 

 where a number of samples of water are examined on the same day, 

 and where in consequence the small plates are in turn removed to a 

 larger sterilised chamber or bell jar, where they may be examined 

 from time to time, at first merely for the number and naked eye char- 

 acteristics of the growths which make their appearance at more or less 

 regular intervals. Inoculations from these growing points may after- 

 wards be made into various nutritive media, bread paste, gelatine, agar- 

 agar, &c. ; careful microscopic examinations must also be conducted. 



Dr. Angus Smith's modification of Koch's solid medium process 

 serves admirably for the demonstration of the number of micro- 

 organisms. He describes the method of working as follows : ^ — 

 " A solution was made containing five per cent, of solid gelatine. 



' Dr. R. Angus Smith "On the examination of Waters.'' Second Report to 

 the Local Government Board, 1884. 



