ESMARCH TUBES. 147 



on top of this box and keep cold water circulating 

 through it. 



ESMAKCH TUBES. The modification of Koch's 

 method which insures the greatest security from con- 

 tamination by extraneous organisms and requires the 

 least amount of apparatus is that suggested by v. 

 Esmarch. It differs from the other methods thus : the 

 dilutions having been prepared in tubes containing 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. 27. 



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. 



Esmarch directs that after completion of the dilu- 

 tions the tops of the cotton plugs in the test-tubes 

 should be cut off flush with the mouths of the tubes and 

 sterilized rubber caps be placed over them. They are 



