446 PLAGUE. 



of soda and then injected. The serum is obtained from the 

 animal in the usual way. Extensive observations with both of 

 these sera show that neither of them can be considered a pow- 

 erful remedy in cases of plague, though in certain instances 

 distinctly favourable results have been recorded. The Indian 

 Commission, however, came to the conclusion " that, on the 

 whole, a certain amount of advantage accrued to the patients 

 both in case of those injected with Yersin's serum and of those 

 injected with Lustig's serum." It may also be mentioned that 

 the Commission found, as the results of experiments, that 

 Yersin's serum modified favourably the course of the disease in 

 animals, whereas Lustig's serum had no such effect. 



3. Serum Diagnosis. Specific agglutinins may appear in 

 the blood of patients suffering from plague, as also they do in the 

 case of animals immunised against the plague bacillus. It is to 

 be noted, however, that in clinical cases the reaction is not in- 

 variably present, the potency of the serum is not of high order,, 

 and the carrying out of the test is complicated by the natural 

 tendency of the bacilli to cohere in clumps. For the last reason 

 the macroscopic (sedimentation) method is to be preferred to the 

 microscopic (p. 109). A suspension of plague bacilli is made by 

 breaking up a young agar culture in .75 per cent sodium chloride 

 solution; the larger flocculi of growth are allowed to settle, and 

 the fine, supernatant emulsion is employed in the usual way. 

 According to the results of the German Plague Commission, and 

 the observations of Cairns made during the Glasgow epidemic,, 

 it may be said that the reaction is best obtained with dilutions of 

 the serum of from i : 10 to I : 50. Cairns found that the date of 

 its appearance is about a week after the onset of illness, and that 

 it usually increases till about the end of the sixth week, there- 

 after fading off. It is most marked in severe cases, character- 

 ised by an early and favourable crisis, less marked in severe 

 cases ultimately proving fatal, whilst in very mild cases it is- 

 feeble or may be absent. The method, if carefully applied, may 

 be of service under certain conditions ; but it will be seen that 

 its use as a means of diagnosis is somewhat restricted. The 

 serum reaction has also been employed to distinguish the plague 

 bacillus from other organisms morphologically resembling it. 



Methods of Diagnosis. Where a bubo is present a little of 

 the juice may be obtained by plunging a sterile hypodermic 



