POTATOES AS CULTURE MATERIAL 45 



Novy and MacNeal's Medium for Culture of Trypanosomes. 1 25 



grammes rabbit or ox flesh is treated with 1000 c.c. distilled water, 

 ;is in making ordinary bouillon, and there are added to the meat 

 extract 20 ^rms. Witt<-'s peptone, 5 grms. sodium chloride, 20 grms. agar, 

 ami in O.C, iiuniial sodium carbonate. The medium is placed in tubes 

 and sterilised in the autoclave at 110 C. for thirty minutes. It is 

 cooled to 50 C., and there is added to the medium in each tube twice 

 its volume of defibrinated rabbit blood, which has been prepared with 

 all asrptic precautions ; the tubes are allowed to set in the inclined 

 position. In inoculating such tubes they are placed in an upright 

 position for a few minutes, and then the infective material is introduced. 



1'otatoes as Culture Material. 



('/) In Potato Jars. The jar consists of a round, shallow, 



glass vessel with a similar cover (vide Fig. 9). It is washed 



with 1-1000 corrosive sublimate, 



and a piece of circular filter paper, 



moistened with the same, is laid 



in its bottom. On this latter are 



placed four sterile watch-glasses. 



Two firm, healthy, small, round 



potatoes as free from eyes as 



possible, and with the skin whole, 



are scrubbed well with a brush 



under the tap arid steeped for two FIG. 9. Potato jar. 



or three hours in 1-1000 corrosive 



sublimate.' They are steamed in the Koch's steriliser for thirty 



minutes or longer, or in the autoclave for a quarter of an hour. 



When cold, each is grasped between the left thumb and forefinger 



(which have been sterilised with sublimate) and cut through the 



middle with a sterile knife. It is best to have the cover of the 



jar raised by an assistant, and to perform the cutting beneath it. 



Each half is put in one of the watch-glasses, the cut surfaces, 

 which are then ready for inoculation 

 with a bacterial growth, being upper- 

 most. Smaller jars, each of which 

 holds half of a potato, are also used 

 in the same way and are very con- 



FIG. 10. -Cylinder of potato 



cut obliquely. (6) By Slices in Tubes. This 



method, introduced by Ehrlich, is the 



best means of utilising potatoes as a medium. A large, long 

 potato is well washed and scrubbed, and peeled with a clean 

 knife. A cylinder is then bored from its interior with an apple 

 corer or a large cork borer, and is cut obliquely, as in Fig 10. 



