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washed again in water and put into a solution of 1 : 500 

 bichloride of mercury for an hour, after which it is cooked in 

 the steam sterilizer for forty minutes on each of two suc- 

 cessive days. Just before inoculation the potato is split into 

 halves by means of a sterilized knife and allowed to fall into 

 a moist chamber cut surface up. 



The moist chamber consists of a double glass dish, the upper 

 one of which is larger than the lower. This chamber should 

 be thoroughly rinsed with a 1 : 500 solution of bichloride of 

 mercury before use. 



Some precautions are necessary to prevent contamination 

 of the potato from external germs. The hand that cuts the 

 potato should be thoroughly sterilized in a 1 : 1000 bichloride 

 of mercury bath. It is better also after washing the potato 

 and before submitting it to the bichloride bath to wrap it in 

 some thin tissue paper, and to keep it in this paper 

 until ready for inoculation. 



Preparation of a Potato for Test-tube Culture. By 

 means of a cork-borer (Fig. 10) a cylinder is cut 

 from a sound potato. This cylinder is cut obliquely 



FIG. 10. 



FIG. 11. 



Nest of cork-borers, used to cut potatoes for test-tube cultures. 



into two pieces, and each placed into a large test- 

 tube (Fig. 11), in which it is sterilized and cooked 

 on three successive days for a half-hour in a steam 

 sterilizer. 



6. Potato-paste is sometimes used for cultivation. 

 For this purpose a potato is boiled, peeled, and 

 mashed with a little sterilized water, placed in a 

 suitable glass dish, and sterilized for one-half hour 

 on three successive days in a steam sterilizer. 



7. Bread-paste is a useful medium for the growth 

 of moulds, and is made in the same way as potato- 

 paste. 



Potato in test- 

 tube. 



