216 OEIENTAL PLAGUE chap. 



It will be seen from this experiment that the agglu- 

 tinating power of the blood serum of this animal (No. 1) 

 showed a gradual increase in degree as time went on, 

 corresponding to the increasing number of injections, but 

 that this proceeded only to a certain point. After a while 

 further injection not only did not enhance this power, but 

 failed to maintain it ; though still later the power became, 

 after additional injection, again restored. These results, 

 qua plague, are quite in harmony with those already 

 obtained in regard of parallel experiments as to agglutinins 

 (with typhoid bacillus, cholera vibrio, and bacillus coli), 

 and as regards also antitoxins with the microbes of 

 diphtheria and tetanus. As in former experiments (I.e. 

 1896-1897) with plague, so now, even a sixth injection was 

 followed by the appearance of a bubo, though the animal 

 remained otherwise lively and fed well. 



This guinea-pig No. 1 will be again referred to at a 

 later stage of this report. 



2. Guinea-pigs Nos. 3 and 4. — These two animals 

 were subjected to repeated injections with at first sterile, 

 later with living culture, of B. pestis ; but the experi- 

 ment diners from the previous experiment in that all 

 injections were made intraperitoneally. Procedure was 

 as follows : — 



[Table 



