44 CLINICAL BACTERIOLOGY AND H^MATOLOGY 



to cut into the yolk. Invert the egg into the wineglass (which 

 must be narrow enough to prevent the egg from dropping 

 down into it), taking- care that none of the lotion touches the 

 cut surface. This is the culture medium, and it is sterilized 

 ready for inoculation. At a pinch it may be incubated in a 

 warm corner near the fire, near the hot-water cistern or other 

 warm place. 



EXAMINATION OF THE CULTURES. 



1. Naked-eye. Each living diphtheria bacillus which has 

 been deposited upon the surface of the culture medium and 

 kept at a suitable temperature will develop into a colony of 

 bacilli ; and these colonies are fairly distinctive, being different 

 from those which are formed by most other organisms. The 

 expert bacteriologist can often give an accurate guess as to 

 the presence or absence of diphtheria bacilli by mere inspection 

 of the cultures. The colonies formed by diphtheria bacilli on 

 solidified blood-serum are small round raised spots; they are 

 variable in size, but rarely exceed that of the head of a medium- 

 sized pin. They are white or grey in colour, and opaque. 

 They do not tend to run together so as to form a uniform film 

 over the surface of the medium, but remain discrete even when 

 closely packed. m Some cocci form colonies which closely 

 resemble those of diphtheria, but they rarely become elevated 

 so high above the surface in the same space of time. 



2. Microscopical. Prepare films by the method described 

 on p. 22, following out all steps in the fullest detail. Stain 

 one of them (step 11) with Loffier's blue or carbol thionin, 

 allowing the stain to act for two minutes, and the other by 

 Gram's method. 



In removing some of the growth to make the film, remem- 

 ber the facts just stated as to the characters of the colonies of 

 the bacillus, and select a colony presenting those characters 

 (especially that of elevation), if one is present. If there is no 

 apparent growth in the tube take " sweeps " of the whole sur- 

 face. This is conveniently done by means of a platinum loop 

 shaped like a stirrup, the flat bar being drawn along the sur- 

 face of the medium from bottom to top, just as a rake is drawn 

 along a flower-bed. 



Now examine your specimens in the way described on p. 27. 



