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Microbes and You 



slight suction to this hole, the chorio-allantoic membrane can be 

 drawn away from the shell membrane. When the shell membrane 

 is removed, the chorio-allantoic membrane is exposed, and the virus 

 inoculum is deposited upon it. To exclude bacterial contamina- 

 tion, the hole in the egg is covered by placing a cover slip over the 



A 



Fig. 72. Methods of inoculating eggs. (A) Inoculation of the yolk 

 sac, a method commonly used for the cultivation of rickettsiae and also of 

 certain viruses, a, air space; sm, shell membranes; s, shell; e, embryo; 

 y, yolk; ys, yolk sac. (B) Inoculation of the chorio-allantoic membrane, 

 a method used for cultivating many viruses, aa, artificial air sac; ca, 

 collapsed air sac; al, allantoic sac; c, chorion; c-am, chorio-allantoic 

 membrane. {Courtesy of E. R. Squibb and Sons, New York.) 



opening. This glass window is held in place by sealing it with a 

 vaseline-paraffin mixture. Some workers prefer to use a strip of 

 scotch tape in place of the cover glass. After suitable incubation 

 the virus particles develop on the membrane and produce foci of 

 growth which might be likened to that of bacterial colonies 

 growing on an agar culture plate. 



Various modifications of the membrane inoculation technic have 



