ESMABOH TUBES. 



137 



passed through it by means of a rubber tube connected 

 with a spigot. The inlet for the water sliould 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 filling 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 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. 28. 



Fig. 28. 



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 keep cold water circulating through it. 



EsMAECH 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 



