viii AGGLUTINATION OF B. PJESTIS 235 



(4) 200 cubic millimetres of plague emulsion were 

 injected into control guinea-pig No. 42. 



The result was this : — Guinea-pigs 42, 39, and 41 died 

 of plague on the fifth day ; guinea-pig 40 died of plague 

 on the sixth day. All the animals had typical bubo and 

 enlarged spleen crowded with plague bacilli. From this 

 it appears that neither the blood nor the spleen of guinea- 

 pig No. 1 were capable of exerting any appreciable 

 germicidal action. That the guinea-pig No. 1 was dis- 

 tinctly protected by September 16 is proved by the fact 

 that an injection on that day of a considerable dose 

 (certainly more than double the ordinary fatal dose) did 

 not cause any illness whatever in this animal. As a 

 matter of fact, some time previous to the above date the 

 guinea-pig did not react on the injection of an otherwise 

 fatal dose of living plague culture. And yet the last- 

 named experiments prove that this animal possessed 

 neither in its blood nor in its spleen those substances 

 (antitoxins, germicidal substances, etc.) which we associate 

 with protection, i.e. substances produced by repeated 

 injections of the microbe, as in diphtheria protection and 

 cholera protection. It is justifiable, therefore, to conclude 

 from the above very striking experiment that, as regards 

 the guinea-pig, the injection (thirteen times) of the plague 

 microbe does not result in the production of demonstrable 

 amounts of anti-bodies — germicidal substances, Pfeiffer's 

 lysins — in the experimental animal. 



The second guinea-pig used for experiment was that 

 already referred to as guinea-pig No. 4, p. 216. 



This animal had been injected at the following 

 periods : — 



