INTRODUCTION 33 



proved to be entirely satisfactory, since the ultrafilter undergoes no 

 change, the membrane remains perfectly transparent, and sterihty is 

 assured. 



Adjust the filtering sac as was directed in the section on "assembling," 

 but instead of fiUing it, and the outside tube, with distilled water, use 

 80 per cent alcohol. On the other hand, in a small autoclave, replace 

 the water by 90 per cent alcohol. Connect the air escape valve of 

 the autoclave to a condenser by means of a rubber tube (simply to 

 prevent the volatilized alcohol from escaping into the laboratory at 

 the beginning of the procedure). Place the ultrafilters, mounted in 

 alcohol, as indicated above, in the autoclave, as for an ordinary steriliza- 

 tion, and start the autoclave as would ordinarily be done. In brief, 

 the sterihzation is accomplished in a vapor of alcohol. When all of 

 the air has been drawn off (this is shown by the fact that the alcohol 

 will commence to distill over and with cooling will condense drop by 

 drop in the condenser) close the exhaust valve, and regulate the source 

 of heat in such a way that the autoclave will have a pressure of i to 

 J of a kilogram per square centimeter. The sterihzation being thus 

 effected in hydrated alcohol, the temperature attained in this way is 

 sufficient. Maintain this pressure for 30 minutes, allowing the auto- 

 clave to remain closed until after coohng is completed. 



This method of sterilization can be applied equally well, whether 

 the collodion ultrafilters are normal (nitrocellulose) or denitrified (pure 

 cellulose) . Except for particular investigations this method of sterihza- 

 tion renders denitrification unnecessary. 



If, as I would advise, one prepares at one time enough ultrafilters 

 for a whole series of experiments they can all be sterilized at one time, 

 and preserved in alcohol just as they come from the autoclave. 



At the time of use, empty the alcohol out aseptically, both from the 

 interior of the sac and from the exterior tube, and replace it with 

 distilled water. Allow the water to remain for 10 to 15 minutes, and 

 then empty this out. Then introduce the fluid to be filtered into the 

 sac (fig. 5). 



With membranes of medium porosity, that is, those most commonly 

 used, allowing ultraviruses to pass with certainty and just as surely 

 retaining the smallest of the bacteria (Asterococcus of pleuropneu- 

 monia, for example), some ten cubic centimeters of ultrafiltrate can 

 be obtained in a few hours (during a night), by simply filling the glass 

 tube supporting the sac with the liquid to be filtered. The shght 

 pressure thus exerted by the liquid in the tube and sac (15 to 20 cc, 

 or even more if desired, since the volume can be increased by simply 



