11 



is variable in its development in the susceptible rabbit and the refractory 

 ■ dog, and is only surely stopped in its development and destroyed by the 

 serum of the rat — a very insusceptible animal. To these observations 

 may be added those of Charrin and Roger,* who found that the rabbit 

 is highly refractory to quarter evil, the guinea-pig most susceptible, yet 

 the microbe of the disease grows more easily in the rabbit's than in the 

 guinea-pig's blood serum. In his studies upon the action of the rat's 

 serum Metchnikofff added a still more adverse case. He discovered 

 that the blood scrum of a rat which had succumbed to anthrax had 

 bictericidal powers equal to that of a rat immune to the disease. 

 Evidently, therefore, there is no constant relationship to be made out 

 between the extent to which an animal is refractory and the degree of 

 the bactericidal power possessed by its blood-serum. Indeed, few satis- 

 fiictory cases have been brought forward in support of such relationship. 

 It has been found that the vibrio Metchnikovi is not killed by the serum of 

 susceptible guinea-pigs, is killed by that of guinea-pigs which have been 

 made refractory^ ; again, that while the growth of the quarter evil 

 microbe is, as above stated, not abundant in guinea-pigs' serum, it is still 

 more scanty in that of the vaccinated guinea-pig,§ and that in the 

 serum of rabbits made refractory towards erysipelas there is as abundant 

 a growth of the streptococcus as in that of normal rabbits, but now the 

 coccus becomes attenuated,ir and similar phenomena are observed with 

 the B. pyocyaneus in rabbits' serum. One or two more examples 

 might be given, but still not enough to prevent there being more 

 exceptions than illustrations in case we attempt to-propound a law as to 

 the direct relationship between immunity and the bactericidal power of 

 the body fluids. 



A further difficulty, to which attention has already been called, is the 

 fact that the destruction of microbes in the extracted body fluids is 

 much more rapid than in the humours within the organism. Not only 

 is it more rapid, but it is more extensive. Thus Lubarsch || obsei'ved 

 that in order to kill a rabbit at least 16,000 virulent anthrax bacilli are 

 required if the injection bo made intravenously — directly into the 

 circulating blood ; a lesser quantity, 10,000, for example, only causes a 

 transient disturbance ; or otherwise, the whole circulating blood can 

 cnly destroy 10,000 bacilli or so at a time. Now, one cubic centimetre 

 of rabbits' blood serum can destroy in a few minutes an equal or even 

 much greater amount. 



* Cliarrin and Roger. — Comptes rcndus dc la Sociile di Biologic, 18S9. 



t ilctchnikoff.—Annalcs de I'lnstitut Pasteur, IS'.tO, p. 193. 



t Behring and Nlseeii.— Zoc. cit.. Coiiarmod by Motschnikoff, Anncdes dc I'lmtitut 

 Pasteur, 1891, September number. 



§ Cbarrln and Roger. — Comptes reandus dc la SociHi de Bioloyie, 1S90. 



% Roger. See Bouchard. " Essai d'une Thuorio do I'lnfection."— X. Internat. Med. Congress, 

 1890. 



II Ln\3a,rach.—CaUralblatt.f. Bacle)-iologie,, VI., 1889, p. 841. 



