132 BACTERIOLOGY. 



ESMARCH TUBES. A useful modification of the 

 plating method just described is that suggested by von 

 Esmarch. It insures the greatest security from contam- 

 ination by extraneous organisms and requires the least 

 amount of apparatus. It differs from the other methods 

 thus : the dilutions having been prepared in tubes con- 

 tain a smaller amount of medium than usual as a rule, 

 not more than 5 to 6 c.c. are, instead of being poured 

 upon plates or into dishes, spread over the inner surface of 



FIG. 26. 



Metal cooling-stage. 



the tubes containing them, and, without removing the 

 cotton plugs, solidified in this position. The tubes then 

 present a thin cylindrical lining of gelatin or agar-agar, 

 upon which the colonies develop. In all other respects 

 the conditions for the growth of the organisms are the 

 same as in flat plates. 



The solidification of the media on the inner sides of 

 the tubes is best accomplished by rolling them upon a 

 block of ice (Fig. 27), after the plan devised by Booker 

 in 1887 in the Pathological Laboratory of The Johns 

 Hopkins University. In this method a small block of 

 ice only is needed. It is levelled and held in position by 



