THE PREPARATION OF CULTURE MEDIA 157 



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, preferably 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, eased 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 any time. It is also possible, though less regularly 

 yielding good results, to sterilize in the inspissator for one day, following 

 this on the second and third days by exposure for thirty minutes to 100 C. 

 in the Arnold steam sterilizer. In doing this, the Arnold should be very 

 gradually heated, at first without outer jacket, this being lowered only after 

 thorough heating has taken place. 



Serum-Water Media for Fermentation Tests. For the determination of 

 the fermentative powers of various microorganisms for purposes of differen- 

 tiation, Hiss has devised the following media in which the cleavage of any 

 given carbohydrate is indicated, not only by the production of an acid 

 reaction, but by the coagulation of the serum proteins. 



Obtain clear beef serum by pipetting from clotted blood in the same 

 way as this is obtained for the preparation of Loeffler's blood-serum medium. 

 Add to this two or three times its bulk of distilled water, making a mixture 

 of serum and water in proportions of one to two or three. Heat the 

 mixture for fifteen minutes in an Arnold sterilizer at 100 C. to destroy 

 any diastatic ferments present in the serum. Add one per cent of a five 

 per cent aqueous litmus solution (the variation in the different litmus 

 preparations as obtained in laboratories necessitates a careful addition of 



