SERUM DIAGNOSIS. 323 



1896 (the former having priority by some weeks), and 

 has already been tested on an extensive scale. The 

 researches which led up to this discovery, and the principle 

 on which it depends, are discussed in the chapter on 

 Immunity. The method is based upon the fact that 

 living and actively motile typhoid bacilli, if placed in 

 the diluted serum of a patient suffering from typhoid fever, 

 within a very short time lose their motility and be- 

 come aggregated into clumps. It would appear that in 

 the progress of the disease certain antagonistic bodies are 

 developed in the blood of the patient, which have a 

 paralysing or devitalising action on the typhoid bacilli. 

 To carry out the method, the two things required are (a) 

 a fluid containing the bacilli in a very actively motile 

 condition, and (^) the diluted blood serum. With regard 

 to the first, either a bouillon culture, preferably not more 

 than twenty-four hours old (certainly not more than forty- 

 eight hours old), should be used ; or a small portion of an 

 agar culture of the same age may be added to a few drops 

 of bouillon in a watch-glass, so as to produce a uniform 

 emulsion. It is useful to note that sufficient growth for 

 the purpose may be obtained within six hours by making a 

 fresh subculture on agar, and incubating at 37 C. ; in 

 such a growth all the bacilli are extremely motile. For 

 the purpose of obtaining the diluted serum several methods 

 have been adopted. The following, used by Delepine, 

 will be found very convenient. A small glass tube, of 

 diameter about one-eighth of an inch, is taken, and two 

 constrictions about half an inch apart are made by heating 

 and drawing out in a flame. In this way a small bulb 

 is formed. The tube is then broken at one of the con 

 strictions and is ready for use. The skin of the patient 

 having been cleansed and dried, a prick is made in the 

 usual way and a drop of blood obtained, which is sucked 

 up into the small bulb. When to be used for transport, the 

 bulb is broken off at the constrictions and the two ends 

 are sealed in the flame. After a time the blood, of course, 

 coagulates within the bulb, but a drop of blood-stained 





