EGG MEDIA 



47 



drops of paraffin on the top of the plug and are incubated in 

 the sloped position. The addition of a sufficient quantity of a 

 solution of basic fuchsin to colour the medium a pale pink is 

 of advantage, as it makes the early growths more easily seen 

 (Cruickshank). 



Glycerin Egg Medium (Lubenau). — 200 c.c. of 5 per cent, 

 glycerin bouillon, 1*5 per cent, acid to phenol-phthalein, are 

 added to ten fresh eggs beaten up, and a're thoroughly mixed. 

 The medium is then treated as above. An equally good medium 

 may be prepared by adding one part of 6 per cent, glycerin, 

 in - 8 per cent, sodium chloride solution, to three parts of 

 beaten egg. 



Potatoes as Cultwre Material. 



Potatoes are best used as slices in tubes, according to the 



method introduced by Ehrlich. 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. 9. Two wedges are thus 



obtained, each of which is placed broad 



end downward in a test-tube of special 

 form (see Fig. 10). In the 

 fo,_ wide part at the bottom of this tube is placed a 

 piece of cotton wool, which catches any condensa- 

 tion water which may form. The wedge rests on 

 the constriction above this bulbous portion. The 

 tubes, washed, dried, and with cotton wool in the 

 bottom and in the mouth, are sterilised before the 

 slices of potato are introduced. After the latter are 

 inserted, the tubes are sterilised in the Koch steam 

 steriliser for one hour, or in the autoclave for 

 fifteen minutes, at 115° C. An ordinary test-tube 

 may be used with a piece of sterile absorbent wool 

 in its bottom, on which the potato may rest. 



Glycerin potato, suitable for the growth of the 

 tubercle bacillus, may be prepared by covering the 

 slices in the tubes with 6 per cent, solution of 

 glycerin in water, and steaming for half an hour. 

 Fig. 10.— The fluid is then poured off and the sterilisation 



Ehrlich's continued for another half-hour. 



tain^' C '° n Potatoes ought not to be prepared long before 



of potato. being used, as the surface is apt to become dry and 



Fig. 9.— Cylinder of 

 potato cut obliquely. 



