130 METHODS OF EXAMINING SEEUM 



Lecithin-Oholestenn Method (Browning, Cruickshank, and Mackenzie).— 

 This method depends on the fact ascertained by them, that a syphilitic 

 serum along with lecithin plus eholesterin fixes more complement than 

 it does along with lecithin alone, whereas this difference does not 

 obtain in other diseases and in the normal condition. Two solutions 

 are thus required, viz. (a) an alcoholic solution of lecithin 1 prepared 

 from ox's liver, and (b) the same lecithin solution plus 1 per cent, of 

 eholesterin. For use two emulsions are prepared, one part of each 

 solution being 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. For each test there are prepared a series 

 of three tubes each containing 0"3 c.c. of lecitbin-cholesterin emulsion 

 and 0"025 c.c. of the serum to be tested, and one of two tubes, each 

 containing 0"3 c.c. of the emulsion of lecithin alone, along with 0/025 c.c. 

 of serum. To the former, complement is added in 4, 6, and 8 doses 

 respectively (i.e., for - 5 c.c. sensitised corpuscles), and to the latter 2 

 and 4 doses. The usual controls must be made. The amount of comple- 

 ment 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 

 suspicions. The method is a very reliable one and has the advantage 

 of being specially delicate in the case of weakly reacting sera. 



The Preparation or 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 

 normal saline. A uniform emulsion is necessary, and if clumps 

 are present these must be disintegrated with a shaking-machine, 

 or deposited by centrifuging. A sample of the living emulsion 

 is withdrawn for the enumeration of the organisms (vide infra), 

 and the vaccine is then sterilised by heating in a water bath at 

 57° C. for one to two hours. With certain staphylococci a 

 longer exposure is advisable, and sometimes in such cases a 

 higher temperature must be employed. It is probable that 

 the lower the temperature at which the contained bacteria 

 are killed the more efficient is the resulting vaccine. The 

 success of the sterilisation must be tested by transferring 



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

 Thomson, Skinner, & Hamilton, Glasgow. 



