438 Chapter XIV 



bacillus in laboratory animals. The blood of the patient becomes 

 " preventive." Against this conclusion the objection has been raised 

 that in the large doses of serum employed by the above observers 

 a protective effect can be obtained, even when using the blood of 

 normal men, i.e. neither suffering from typhoid fever, nor having 

 recovered from this disease. Later researches, however, have con- 

 firmed the observation made by Chan tern esse and Widal. It is no 

 doubt true that the injection of half a cubic centimetre of normal 

 human serum into the peritoneal cavity of an untreated guinea-pig is 

 often sufficient to render it refractory to a dose of typhoid cocco- 

 bacilli fatal to the control animal. We have an ordinary protective 

 action, such as described in Chapter x. The blood of typhoid 

 patients is, however, capable of protecting normal animals, in doses 

 which exhibit not the slightest protective action if normal blood be 

 used. 



The protective power of the blood serum of convalescents has been 

 studied very carefully by Pfeiffer and Kolle 1 . In certain individuals 

 very small quantities (0*001 c.c.) of this fluid were quite sufficient to 

 confer on guinea-pigs an immunity against fatal typhoid peritonitis. 

 This power was at its maximum only during the first weeks of con- 

 valescence. In one case, in which these observers were able to study 

 the properties of the blood on two separate occasions, they found 

 that two months after the first examination there had been a marked 

 falling off in the acquired protective power. In a second case, where 

 the blood was examined a year after the patient had recovered from 

 a grave attack of typhoid fever, they found only feeble indications 

 of this specific protective property. " Everything seems to indicate," 

 conclude Pfeiffer and Kolle, " that the protective typhoid substances 

 were rapidly eliminated by the blood stream. If further researches 

 should confirm these results, as yet few in number, we might conclude 

 therefrom that the immunity which, after an attack of typhoid fever, 

 [460] persists for years, frequently even for the rest of life, would be in- 

 dependent of the amount of ready-prepared protective substances 

 in the blood" (l.c. p. 218). The facts upon which this conclusion is 

 based confirm the general thesis that even acquired immunity is in 

 no way the function of any humoral property. 



We know that in the protective serums there is constantly found 

 the specific fixative (the sensibilising substance of Bordet, the inter- 

 mediary body or amboceptor of Ehrlich). It was, therefore, quite 

 1 Ztschr.f. Hyg., Leipzig, 1896, Bd. xxi, S. 213. 



