APPENDIX. 405 



sterilizers and inspissators may also be obtained from the apparatus makers. 

 Blood serum so sterilized may be used in various ways. It may be rendered 

 solid with the tube in an upright position, or when a large surface is required 

 in an oblique position, by placing the tube on the sloping floor of a warm 

 chamber. This slope should be such that the blood serum does not come 

 within an inch of the wadding plug. To bring about the solidification the 

 temperature should be kept between 65 and 68 C., at which temperature 

 solidification takes place slowly, but the serum remains comparatively clear. 

 Sheep's blood coagulates more rapidly than that of the calf, the time required 

 varying from half an hour to an hour, according to the temperature that is 

 maintained. In place of test tubes, watch glasses or covered glass dishes may 

 be used to hold the serum. As the serum cools there collects in the tube a 

 quantity of condensed vapour ; this, however, may be prevented by adding a 

 small quantity (i per cent.) of gelatine or 6 to 8 per cent, of glycerine. This 

 latter prevents the formation of a dry scaly surface, and at the same time 

 absorbs a considerable proportion of the condensed vapour. When glycerine 

 is added the temperature required to bring about solidification is over 75 or 

 78 C. 



Loffler's Serum Medium. 



Loffler added to three parts of blood serum one part of the flesh infusion 

 already described, I per cent, of peptone, I per cent, of grape sugar, and 

 5 per cent, of common salt. The meat broth, prepared as above described 

 (p. 399), is allowed to cool down to 50 C., and is then mixed with the serum. 



HueppJs Agar Serum. 



Hueppe uses a mixture of blood serum and agar-agar for plate cultiva- 

 tions, especially where he wishes to use the plate method for the separation 

 of the tubercle bacilli. He takes the sterilized serum at a temperature of 

 37 C., inoculates it, and shakes it thoroughly in order to distribute the 

 organisms through it ; he then pours it into the fluid agar-agar meat peptone 

 solution at 42 C. ; the mixture is again well shaken to continue the distri- 

 bution of the germs equally through the fluid, and then either plate, tube, 

 or flask cultivations are made ; the mass is allowed to become solid, after 

 which it is kept at the temperature of the body (about 37 C.), at which 

 temperature it remains perfectly solid. 



To Fill Test Tubes or Flasks with Fluid Media. 



Before transferring fluid gelatine or agar-agar meat broth or other fluid 

 media to test tubes or flasks, these should be previously plugged and 

 sterilized, as mentioned on p. 399. With a sterilized pipette (see p. 389) 

 the fluid is run into these vessels, the plug is returned, and the vessels with 

 the contained nutrient medium are sterilized for ten minutes or a quarter 

 of an hour on each of two successive days. As soon as the vessels are 

 taken from the steamer the plugs are covered with sheets of sterilized paper, 

 which are kept in position by string or indiarubber bands. 



In place of the sterilized pipette a small carefully-sterilized funnel may be 

 used. The stem of this is simply inserted into the flask or test tube, and the 

 amount of the medium required is poured in from small stock flasks. A burette 

 with a small funnel may be used in the same way, or better still, the stock 

 flasks may be fitted with an indiarubber bung in which are bored two 

 holes. Through one of these holes is introduced a glass tube, at one end 



