APPENDIX. 401 



Soyka's Ground Rice Medium. 



A medium which can be used instead of bread paste is that described by 

 Soyka. It is composed of ground rice, 10 grammes ; milk, 15 cc. ; neutral 

 beef bouillon, 5 cc. These ingredients are thoroughly mixed, and put into 

 small covered glass dishes or small glass flasks, which are sterilized, as is 

 the bread paste. It forms a beautiful solid white opaque mass, on which 

 coloured organisms may be even more easily studied than when they are 

 grown on bread paste." 



Sueppe's Method of Cultivating on Egg Albumen. 



Eggs may also be used as culture media. The yolk is broken down and 

 mixed with the white by means of thorough shaking (or the white only 

 may be used, in which case the yolk is left unbroken) ; the shell is then 

 disinfected with bichloride of mercury solution, a hole is chipped at one 

 end, and the membrane cut through with a pair of sterilized scissors. The 

 inoculation is made with a pipette or a platinum needle, and then the open- 

 ing is covered with a piece of sterilized cotton wadding or paper, which is 

 painted over and sealed with surgical collodion. 



Potatoes. 



The simplest and most effective way in which potatoes can be used as 

 solid culture media is by introducing small wedge-shaped strips into sterilized 

 test tubes. All that is here necessary is to clean the potato thoroughly, then 

 steam it for five minutes, allow it to cool, and, with a cork-borer or apple- 

 corer, cut out a cylinder from the longest diameter, remove the two ends of 

 the cylinder with a knife, and cut obliquely across from end to end, so that 

 two wedge-shaped portions are formed ; each of these is put into a test tube, 

 prepare'd as follows : — Into a plugged test tube, sterilized by dry heat, a 

 small piece of sterilized cotton wadding, well moistened with distilled water, 

 is introduced and pushed to the bottom ; the potato wedge is then intro- 

 duced so that the base rests on the surface of the moist wadding. The 

 whole is boiled in the steam sterilizer for at least three quarters of an hour 

 (better an hour or an hour and a half), when it is ready for use. 



If test tubes are not readily obtainable, a soup-plate and a basin, well 

 washed and rinsed with a i per i ,000 solution of bichloride of mercury may 

 be used as a sterile chamber, a couple of layers of blotting-paper soaked with 

 the bichloride solution being placed in the soup-plate, on to which any 

 organisms in the air under the basin may fall after the sterilizing process 

 has been completed and the parts of the apparatus placed in position. 

 A clean and smooth-skinned potato is thoroughly scrubbed, and the eyes 

 and any diseased portions are removed with a sharp-pointed knife ; it is 

 then soaked for fifteen minutes in a i per 1,000 solution of bichloride 

 of mercury, after which it is washed in water, wrapped in paper, and 

 steamed for half an hour ; at the end of twenty-four hours it may again 

 be steamed for fifteen minutes, and allowed to cool. (A single steaming 

 is, however, usually sufficient.) The hands are carefully washed first in 

 soap and water, then in a I per 1,000 sublimate solution. A knife is 

 sterilized by heat in a naked flame, or in the hot-air chamber at 150° C. (in 

 the latter case it should first be wrapped in cotton wadding or in paper), 

 and then allowed to cool. The potato is taken in the left hand, and, with 

 the sterilized knife, is cut through the middle, and the two halves are intro- 



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