ESMARCH'S TUBES. 119 



without sterilizing the needle it is passed thoroughly 

 over the surface of the medium in tubes 2, 3, 4, etc., 

 etc., in succession. When development has occurred 

 essentially the same conditions as regards separation of 

 the colonies will be found as is the case when plates are 

 poured. If a slanted medium be employed, about the 

 most dependent angle of which water of condensation 

 has accumulated, as blood-serum, agar-agar, and potato, 

 the dilutions may be made in this fluid, and this is then 

 to be carefully smeared over the solid surface of the me- 

 dium. The tubes thus treated should be kept in an up- 

 right position to prevent the fluid from flowing over the 

 surface. When sufficiently developed, single colonies 

 may be isolated from tubes prepared in this manner 

 with comparative ease. (See also method for the isola- 

 tion of b. diphtherice on blood-serum.) 



