462 



CONTROL OF CULTURES 



finally recovered from the sixth flask, they are in an entirely closed sys- 

 tem. After injection, the Protozoa are allowed to migrate to the narrow 

 top of the flask and, when large numbers have collected, they are forced 

 over into the bottom of flask 2 by a volume ( 1-2 ml.) of sterile medium 

 from the liter reservoir. After each migration the process is repeated, 

 and the fluid drained from the system at the top of flask 6 is kept in 



Figure 126. Migration-dilution apparatus drawn to show construction. AH flasks are 

 filled with fluid and sterilized. After cooling, the Protozoa to be sterilized are injected 

 through the vaccine port of flask 1. Successive migrations result, and the Protozoa are 

 finally collected in the test tube from flask 6. (From ClaflF, 1940.) 



sterile test tubes and used as bacteriological controls on the fluid going 

 before the Protozoa. The first Protozoa collected in the sixth tube are 

 then separated into the various culture media. 



The chief advantages of this apparatus are the simplicity of operation 

 and the reduction of chance contamination. The whole apparatus is as- 

 sembled in a compact unit and can be sterilized partially full of medium. 

 Completion of the filling of the flasks is carried out after cooling, ex- 

 treme care being taken to expel all air bubbles. No air bubbles may be 

 allowed to enter during the injection of the contaminated Protozoa, as 

 these will practically always rise ahead of the migration and contaminate 

 every flask in order. 



Clafif gives experimental evidence for the sterilization of Paramecium, 

 Tillina, Tetrahymena and Glaucoma in this apparatus. It has been used 

 on numerous occasions in this laboratory and found to be very satisfac- 



