THE PREPARATION OF CULTURE MEDIA 131 



fifteen minutes in an Arnold sterilizer. It is then set away in the ice 

 chest for about twelve hours in order* to allow the cream to rise. Milk 

 and cream are then separated by siphoning the milk into another 

 flask. It is rarely necessary to adjust the reaction of milk prepared in 

 this way, since, if acid at all, it is usually but slightly so. If, however, 

 it should prove more than 1.5 per cent acid, it should be discarded 

 or neutralized with sodium hydrate. The milk may then be poured 

 into test tubes without further additions, or litmus solution may be 

 added in a quantity sufficient to give a purplish blue color. The 

 tubes are sterilized by fractional sterilization in the Arnold sterilizer for 

 thirty minutes on three successive days. 



Serum Media. Loeffler's Medium. Beef blood is collected at the 

 slaughter house in high cylindrical jars holding two quarts or more. 

 It is desirable that attempts should be made to avoid contamination 

 as much as is feasible by previously sterilizing the jars, keeping them 

 covered, and exercising care in the collection of the blood. 



The blood is allowed to coagulate in the jars, and should not be 

 moved from the slaughter house until coagulated. All unnecessary 

 shaking of jars should be avoided. As soon as the coagulum is fully 

 formed, adhesions between the clot and the sides of the jar should be 

 carefully separated with a sterile glass rod or wire. The jars are then 

 set away in the ice chest for 24 to 36 hours. At the end of this time 

 clear serum will be found over the top of the clot, and between the clot 

 and the jar. This should be pipetted off, preferably with a large pipette 

 of 50 to 100 c.c. capacity, or siphoned off with sterile glass tubing, and 

 transferred to sterile flasks. 



To three parts of the clear serum is then added one part of a one 

 per cent glucose beef infusion or veal infusion bouillon. The mixture is 

 filled into tubes, perferably the short test tubes commonly used for 

 diagnostic diphtheria cultures. The tubes are then placed in a slanting 

 position in the apparatus known as an inspissator (see p. 71). This is 

 a double-walled copper box covered by a glass lid, cased in asbestos, 

 and surrounded by a water jacket. It is heated below by a Bunsen 

 flame. Together with the tubes a small open vessel containing water 

 should be placed in the inspissator to insure sufficient moisture. The 

 temperature of the inspissator is now raised to 70-75 C., care being 

 taken that the rise of temperature takes place slowly. The temperature 

 is maintained at this point for two hours, and the process is repeated, for 

 the same length of time, at the same temperature, on six successive 

 days, preferably without removing the tubes from the inspissator at 



