272 Chapter IX 



of serums; he has laid special stress on the essential difference 

 between the influence of normal serums and of those obtained from 

 animals that have acquired immunity. Whilst, in order to obtain 

 a protective effect with the normal blood or serum of man and 

 animals, it is necessary to inject a considerable quantity (from 

 0*5 c.c. upwards), the specific serum, i.e. serum obtained from 

 persons recovered from cholera or from animals vaccinated against 

 the cholera vibrio, is active in a very minute dose. Sometimes the 

 cholera peritonitis of the guinea-pig is prevented by a fraction of 

 a milligramme of such serum ^ Based on these facts, Pfeiffer has 

 expressed the view that the normal serum acts by stimulating 

 the natural powers of defence of the animal, whilst the specific 

 serum exercises its influence in virtue of the property of causing 

 the formation of a special secretion which acts only against the 

 micro-organism which served for the production of the immunity. 

 Pfeiffer and his collaborators have demonstrated that normal serums 

 are protective, not only against the cholera vibrio, but also against 

 several other micro-organisms, e.g. the typhoid bacillus. One of his 

 [286] pupils, Voges^, believed that, in certain infections, the protective 

 power of normal blood might be greatly exaggerated, and that, 

 in these cases, the limit between the activity of normal and of 

 specific senims might be almost completely effxiced. He affirmed, 

 especially, that very small doses (0*]. c.c.) of blood serum from 

 a normal guinea-pig was quite sufficient to prevent, in other guinea- 

 pigs, a fatal infection by the micro-organism of hog cholera and 

 its allies. As this fact might be of general application I asked 

 M. Saltykoff"^, who was working in my laboratory, to verify the 

 statements of Voges. Several series of experiments demonstrated 

 the incorrectness of the contention. The small doses of normal 

 serum of guinea-pigs, indicated by Voges, were found to be ab- 

 solutely incapable of protecting against the virus used by him in 

 his experiments. 



The fact that normal serums, injected in sufficiently large doses, 

 exhibited an undoubted protective property, affords additional 

 proof that this property cannot be identified with the fixative 

 power. The latter was present in serums which were not pro- 

 tective ; here, then, we have the inverse phenomenon and we see 



1 See Lazarus, Berl klin. Wchnschr., 1892, S. 1072. 



2 Ztschr.f. Hyg., Leipzig, 1896, Bd. xxiii, S. 149. 



2 Ann. de VInst. Pasteur, Paris, 1902, t xvi, p. 94. 



