PREPARATION OF MEDIA 93 



is drawn from the clots with sterile pipettes and either dis- 

 tributed at once into tubes or else stored with 0.25 to 0.3% 

 chloroform added. Discontinued sterilization is rendered un- 

 necessary. The temperature required to produce a suffi- 

 ciently firm and yet not too hard and dry serum is for the 

 dog 75 to 76 C. For horse serum it is from 4 to 5 lower. 

 The serum is set in a thermostat into which a large dish of 

 water is always placed to forestall any abstraction of 

 moisture from the serum. About three hours are required 

 for the coagulation. When serum containing chloroform is 

 to be coagulated, the tubes should be placed for an hour or 

 longer in a water bath at 55 to 60 C., or under the receiver 

 of an air pump, to drive off the antiseptic. This procedure 

 dispenses with all sterilization excepting that going on dur- 

 ing the coagulation of the serum. It prevents the gradual 

 formation of membranes of salts, which, remaining on the 

 surface during coagulation, form a film unsuited for bacteria. 

 Tubes of coagulated serum should be kept in a cold closed 

 space where the opportunities for evaporation are slight. 

 They should always be kept inclined. 



The ordinary cotton-plugged test tubes are not used, be- 

 cause of the rapid drying, but a tube is used which has a 

 ground glass cap fitted over it. This cap contracts into a 

 narrow tube plugged with glass wool. This plug is not dis- 

 turbed. The tube is cleaned, filled and inoculated by remov- 

 ing the cap. 



Agar-gelatin-serum. This medium was introduced by 

 Bang 1 and Stribolt for the investigation of certain anaerobic 

 bacteria. After having liquefied the agar-gelatin (that is to 

 sa 7^ 34 P er cent agar and 5 per cent gelatin) the liquid is 

 cooled to 45 C., and it is then mixed with about half its 

 volume of liquid sterile serum. The serum should be added 

 just before the medium is to be used.* 



1 Bang. The Jour, of Com par. Path, and Therap., Vol. X (1897) 

 p. 125. 



* A tube of the liquid medium is inoculated with a loopful of 

 the material from the first, a second tube is inoculated with 2 to 3 



