362 



Journal of Applied Microscopy. 



Fig. -S. 



gas is then started under the steriUzer, and if the corks have been tightly shoved 

 in and firmly tied no watching of the serum is required. 



Within from ten to twenty minutes from the time of getting up steam (accord- 

 ing to the amount of serum in the tubes, the size of the gas flame, and the com- 

 position of the mixture — pure blood-serum 

 or Loefifler's medium), the serum will be 

 found coagulated evenly and without any 

 disfiguring bubbles. 



The mode of action of the cork is simple. 

 By it, air of room temperature is closely 

 confined in the tube. As it becomes heated, 

 this air, tending to expand, increases the 

 pressure in the tube, and hence it is im- 

 possible for boiling to take place at 100° C, 

 the temperature of the sterilizer. 



The tubes should be left in the sterilizer 

 for half an hour, in order to insure thor- 

 oughness of the first sterilization. Just 

 here is another advantage of the cork. 

 Without it prolonged action of heat dries out a portion of the serum along 

 the thin slanting edge. With it this occurs to only a very insignificant extent 

 even if left in the sterilizer for a considerable time. The tubes are similarly 

 steamed on the two subsequent days, after which they may be put aside and will 

 keep indefinitely. I have now on hand slants of Loeffler's blood-serum mixture 

 made eighteen months ago and they are still in perfect condition, the cork pre- 

 venting evaporation. 



Where a large number of tubes is required, a wire apparatus could be easily 

 constructed wherein several tiers of tubes could be arranged on the proper slant, 

 but this I have never found necessary ; for the process, after the tubes are 

 properly plugged, requires no special skill, and even the laboratory boy can be 

 trusted to remove one batch and place another in the sterilizer. 

 To summarize the advantages of the method above described : 



1. A perfectly smooth culture surface is secured without the necessity of 

 close supervision during coagulation. 



2. Coagulation is accomplished in from ten to twenty minutes. 



3. The medium does not become dried out during the processes of coagula- 

 tion and sterilization. 



4. Sterilization is conducted at a high temperature, thus insuring thorough- 



5. The culture medium does not subsequently dry out, but may be kept 

 indefinitely. 



The only disadvantage I have found connected with the method is that a tube 

 with a cork and a deep-seated cotton plug is not so easy to manipulate when 

 making cultures as is one closed in the usual way. This inconvenience is slight 

 and does not weigh against the many advantages. 



It is well when going to the slaughter-house to obtain a sufficient quantity of 



