108 BACTERJOLOQY. 



5 to 6 c.c. — are, instead of being poured out upon plates 

 or into dishes, spread over the inner surface of the tube 

 containing them, and without removing the cotton plugs 

 are caused to- solidify 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 dilutions 

 the tops of the cotton plugs in the tubes should be cut 

 oif flush with the mouth of the test-tube and a steril- 

 ized rubber cap be placed over this. They are then to 

 be held in the horizontal position and twisted between 

 the fingers upon their long axes under ice-water. The 

 gelatin becomes solidified thereby and adheres to the 

 sides of the tube. When the gelatin is quite hard the 

 tubes are removed from the water, wiped dry, the.rubber 

 caps removed, and they are set aside for observation. 



For some time past we have deviated from the direc- 

 tion given by v. Esmarch for this part of his method, 

 and instead of rolling the tubes under ice-water, we roll 

 them upon a block of ice (Fig. 25), after the method 

 devised by Booker in the Pathological Laboratory of 

 the Johns Hopkins University in 1887. In this method 

 a small block of ice only is needed. It is arranged 

 nearly level, and is held in position by being placed in 

 a dish upon a cloth. A horizontal groove is melted in 

 the surface of the ice with a test-tube of hot water. The 

 tubes to be rolled are then held in an almost, not quite, 

 horizontal position and twisted between the fingers 

 until the sides are moistened by the contents to within 

 about 1 cm. of the cotton plug, care being taken that 

 the gelatin does not touch the cotton ; otherwise the latter 



