ESMARCWS TUBES. 115 



means of a rubber connection with a spigot. The 

 inlet for the water should be just above the bottom 

 of the box, and the outlet just beneath the top and 

 slightly turned upward and then downward, so as to 

 insure the complete filling of the space with water. The 

 box should be sufficiently strong to resist the pressure of 

 the water. A convenient size is from 20 to 25 cm. in 

 diameter, and of about 1.5 to 2 cm. high. It is simple 

 in construction, and can be made by any copper spinner. 

 An idea of its construction is given in Fig. 25. 



FIG. 25. 



Metal cooling-stage. 



When gelatin or agar-agar is to be cooled it is only 

 necessary to place the dishes containing it on top of this 

 box and start cold water circulating through it. 



ESMARCH'S TUBES. The modification of Koch's 

 method which insures the greatest security from con- 

 tamination by outside organisms and requires the small- 

 est supply 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 out upon plates 

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



