TUBES 



141 



TUBES. 



Esmarch Tubes. — ^A useful modification of the plating 

 method just described is that suggested by von Esmarch. 

 It insures the greatest security from contamination by 

 extraneous organisms and requires the least amount of 

 apparatus. It differs from the other methods thus: the 

 dilutions having been prepared in tubes contain 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 the tubes containing 



Fig. 26 



Metal cooling stage. 



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 Univer- 

 sity. In this method a small block of ice only is needed. 



