52 SOLID MEDIA 



1. Lay the tubes, each containing about 10 c.c. of serum, in the sand. Incline 

 the apparatus so that the serum does not touch the plugs. 



2. Light the gas, and when the temperature as shown by the thermometer inside 

 reaches 68 C., adjust the regulator (Chap. III.), so that the temperature remains 

 constant. 



3. The length of time required to solidify different samples of serum varies (from 

 2 to 3 hours). A tube must be taken out from time to time to ascertain the con- 

 dition of the serum, which will be sufficiently set when holding the tube upright it 

 retains its slope. [It is perhaps better to hold the tube by the upper end and tap 

 the lower end firmly against the thumb nail : if the serum quiver, the heating has 

 not been continued long enough.] Stop the heating at this stage. The serum 

 when set should still be transparent and of an amber-yellow colour. 



To obtain a more transparent product, Vagedes advises coagulating in an atmosphere 

 of water vapour, and this can be effected by placing Petri dishes filled with water along- 

 side the tubes, [or by placing folded cloths which have been wrung out in warm water 

 over the tubes, taking care that they do not touch the wool plugs.] 



4. Incubate at 30 [or 37] C. for 36 hours, to ensure their sterility before using 

 them as culture media. 



If only a few tubes of serum have to be coagulated, Koch's apparatus can be dispensed 

 with, and the tubes dealt with as follows. Arrange the tubes in a small flat copper tray 

 (fig. 42), about 12 cm. wide, one side of which is notched to receive the upper plugged 



FIG 42. Copper tray on which to slope tubes of culture media. 



ends of the tubes, while the other ends resting against the opposite side keep the tubes 

 in a sloped position. Cover the tray with a sheet of glass, stand it on a saucepan filled 

 with water, and slowly heat the water to boiling. The tubes will be set in about an 

 hour or two. 



Other serum media. 



In cases of simple pleurisy the fluid which can be drawn off often yields 

 a very clear, easily coagulable serum, very suitable for the purposes of a 

 culture medium. 



To collect the fluid aseptically, operate in the usual manner, using a sterile 

 Potain's apparatus. Boil the trocar, autoclave the rubber plug and aspirating 

 tube at 115 C., and sterilize the flask [or bottle] in the hot air sterilizer. The 

 serum is distributed into tubes afterwards by means of a Chamberland 

 flask (see also p. 45). An absolutely sterile serum can frequently be obtained 

 in this way, but it is nevertheless often necessary to tyndallize the fluid 

 before coagulating it (p. 47). 



Ascitic fluid as a rule yields only a poorly coagulable serum, which is not 

 of great value when a solid serum is wanted. 



Lceffler's serum. 



1. Prepare a broth in the ordinary way, using 



Water, - - - 1000 grams. 



Beef, - - 500 



Peptone, - - 20 



Salt, - 5 



Glucose, - 10 



Normal soda solution, - - - Q.S. to make slightly 



alkaline. 



2. Aspirate 1 part of this broth and 3 parts of sterile liquid serum into a 

 Chamberland flask. 



