ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



407 



oil-immersion objective, and is specially recommended for use in the 

 tropics, or where the ordinary electric current is not available. 



Fig. 54. 



B. Technique.* 

 (1) Collecting* Objects, including- Culture^Processes. 



New Method of Sterilizing Bacterial Cultures.f — H. Stassano 

 points out that in sterilizing a broth culture or an emulsion of a bacterium 

 in physiological salt solution, the fluid is subjected to unequal heating, 

 and that in order for the whole of the fluid to attain the indicated 

 lethal temperature the heating must be unnecessarily prolonged. The 

 length of time to ensure sterilization at the given temperature will 

 depend upon (1) the volume of fluid to be sterilized, and (2) the con- 

 centration of organisms in suspension. The author has devised a rapid 

 method of sterilization in which the culture or the emulsion traverses, 

 under the constant and regular pressure of an inert gas (e.g. nitrogen), 

 an extremely narrow rectangular cell, formed by the approximation of 

 two flat bronze plates, which are separated by a frame of Japanese paper 

 T ^j mm. in thickness, the frame and opposed plates being held to- 

 gether by screws. The apparatus is immersed in a double-boiler at the 

 required temperature, and the fluid, the sterilization of which is desired, 

 is slowly forced through the cell by the pressure of the inert gas. By 

 this means a constantly changing film of the liquid, ^mm. in thickness, 

 is brought into contact with the bronze plates, which remain constantly 

 at the required temperature. 



This method of sterilization is particularly recommended in the 

 preparation of vaccines, as the least amount of injury to the contained 

 antigen, consistent with sterilization, is claimed to be obtained. The 



* This subdivision contains (1) Collecting Objects, including Culture Pro- 

 cesses ; (2) Preparing Objects ; (3) Cutting, including Embedding and Microtome ; 

 C4) Staining and Injecting ; (5) Mounting, including slides, preservative fluids, etc. ; 

 (6 ) Miscellaneous. t Comptes Rendus, clx. (1915) pp. 820 2. 



