SERUM MEDIA. 49 



be laid on their sides without the contents reaching as 

 high as the plug. The serum tubes being thus placed, 

 and the temperature being raised to 65 C., the contents 

 solidify in a sloped position in the interior. It is well not 

 only to have the jacket filled with water, but also to 

 put some water in the trough in which the tubes lie, 

 (and also to have a thermometer in the latter). This 

 prevents cooling of the tubes when the lid is raised to 

 see if the process is complete. It is evident that this 

 medium is tedious to prepare, but it was necessary as 

 long as no other means for growing the tubercle 

 bacillus was known. Pleuritic and other effusions may 

 be prepared in the same way, and used as media, 

 but care must be taken in their use, as we have no right 

 to say that pathological effusions have the same chemical 

 composition as normal serum. 



If blood be collected with strict aseptic precautions, then 

 sterilisation of the serum is unnecessary. To this end the 

 mouth of the cylinder used for collecting the blood, instead 

 of being plugged with wool, has an india-rubber bung 

 inserted in it through which two bent glass tubes pass. 

 The outer end of one of these is of convenient length and, 

 before sterilisation, a large cap of cotton wool is tied over 

 it ; the other tube is plugged with a piece of cotton wool. 

 In the slaughter-house the cap is removed and the tube 

 is inserted into the blood vessel as a cannula. The cylinder 

 is thus easily filled. Another method is to conduct the 

 blood to the cylinder by means -of a sterilised cannula and 

 india-rubber tube, the former being inserted in the blood 

 vessel. The serum obtained under such circumstances 

 must be incubated before use, to make sure that it is sterile. 



Alkaline Blood Serum (Lorrain Smith's Method). To 

 each 100 c.c. of the serum obtained as before, add 1-1.5 c - c - 

 of a i o per cent solution of sodium hydrate and shake it 

 gently. Put sufficient of the mixture into each of a series 

 of test-tubes, and laying them on their sides, sterilise by 

 method B (2). If the process of sterilisation be carried 

 out too quickly, bubbles of gas are apt to form before 

 4 



