ESMARCH TUBES. 135 



With a platinum needle a bit of the stibsrance to be 

 studied is smeared upon tube No. 1 ; without sterilizing 

 the needle it is passed in succession over the surface 

 of the medium in tubes Nos. 2, 3, 4, etc. When de- 

 velopment has occurred essentially the same conditions 

 as regards separation of the colonies will be found as 

 when plates are poured. If a slanted medium be em- 

 ployed, 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 medium. The tubes thus treated 

 should be kept in an upright position to prevent the 

 fluid flowing over the surface. When sufficiently de- 

 veloped, single colonies may be isolated with compara- 

 tive ease from tubes prepared in this manner. (See also 

 method for the isolation of bacillus diphtherise on blood- 

 serum.) 



