134 METHODS OF EXAMINING SERUM 



amount observed in the controls. Some observers use the same 

 amount of complement in each tube, but vary the amounts of 

 suspected serum, and in this way some idea of the deviating 

 power of the serum is obtained, but we consider that the method 

 given is to be preferred. 



Lecithin-Cholesterin Method (Browning, Cruickshank, and 

 Mackenzie). This method depends on the fact ascertained 

 by them, that a syphilitic serum along with lecithin plus 

 cholesterin fixes more complement than it does along with 

 lecithin alone, whereas this difference does not obtain in other 

 diseases and in the normal condition. A "75 per cent, alcoholic 

 solution of lecithin x prepared from ox's liver is made up and 

 to this is added 1 per cent, of cholesterin. For use, one part of 

 the solution is floated on the surface of seven parts of *85 per 

 cent, sodium chloride solution and then mixed slowly by rotating 

 the tube, so as to give a turbid emulsion. To each of a series of 

 tubes *6 c.c. of the emulsion is added along with '05 c.c. of the 

 serum to be tested ; a similar series is prepared with a similarly 

 prepared emulsion of lecithin alone. The amount of complement 

 absorbed in the two series is estimated, as above described. A 

 difference of five doses is practically conclusive as to the presence 

 of syphilis, whilst a difference of three doses is to be regarded as 

 very suspicious. The method is a very reliable one and has the 

 advantage of being specially delicate in the case of w r eakly 

 reacting sera. 



In the case of all the methods mentioned a normal serum 

 ought always to be used as a control, and when there is any 

 doubt as to the efficiency of the reagents a known syphilitic 

 serum should be used as a further control. 



THE PREPARATION OF VACCINES. 



During recent years, in consequence of the work of Sir 

 Almroth Wright, the method of treating bacterial disease by 

 vaccines has been very much developed. The general principle 

 is to inject into the infected individual an emulsion of dead 

 bacteria. In certain cases the bacteria are subjected to dis- 

 integrating processes before being used, but most frequently the 

 vaccines simply contain killed bacterial cells, and the preparation 

 is comparatively simple. 



In the case of ordinary organisms, e.g.^ pyogenic cocci, b. coli, 

 etc., the growth from a young sloped agar culture is emulsified in 



1 The lecithin-cholesterin and lecithin solutions can be obtained from Messrs. 

 Thomson, Skinner, & Hamilton, Glasgow. 



