572 IMMUNITY 



these the two first are concerned with the protective property 

 of an antibacterial serum. 



(a) Bactericidal and Lysogenic Action. — Pfeiffer found that 

 if certain organisms, e.g., the cholera spirillum, were injected 

 into the peritoneal cavity of a guinea-pig highly immunised 

 against these organisms, they lost their motility almost immedi- 

 ately, gradually became granular, swollen, and then disappeared 

 in the fluid — these' changes constitute what is now generally 

 known as " Pfeiffer's phenomenon " or bacteriolysis. It was 

 subsequently shown, however, by Metchnikoff and by Bordet 

 that bacteriolysis might occur outside the body by the addition 

 of fresh peritoneal fluid or normal serum to the heated immune- 

 serum. Pfeiffer also found that an anti-serum heated to 70° C. 

 for an hour produced the reaction when injected with the 

 corresponding organisms into the peritoneum of a fresh animal. 

 The outcome of these and subsequent researches is to show that 

 when an animal is immunised against a bacterium, there appears 

 in its serum an anti-substance, which is generally known as 

 immwne-body, amboceptor (Ehrlich), or substance sensibilisatrice 

 (Bordet), is comparatively stable, resisting usually a temperature 

 of 70° C., for an hour. It cannot produce the destructive effect 

 alone, but requires the addition of a substance normally present 

 in the serum, which is spoken of under various names — com- 

 plement (Ehrlich), alexin or cytase (French writers). The com- 

 plement is relatively unstable, being rapidly destroyed by a 

 temperature of 60° C, and it is not increased in amount during 

 the process of immunisation. Though ferment-like in its in- 

 stability, it differs from a ferment in being fixed or used up 

 in definite quantities. 



Observation has shown that complement is not a single substance, 

 but is really made up of two components. Ferrata, who was the first to 

 establish this fact, employed the following method : Fresh gainea-pig's 

 serum is dialysed against running water for twenty-four hours ; the 

 precipitate which has formed at the end of that time is separated by the 

 centrifuge, washed several times in distilled water, and then dissolved in 

 normal salt solution. The separated fluid is passed through thick filter 

 paper. The component in the solution of the precipitate unites directly 

 with sensitised corpuscles — and then that in the separated fluid enters 

 into combination ; hence they have been called by Brand "middle-piece" 

 and "end-piece" respectively. The separation by such a method is, 

 however, far from being a complete one. The method of Liefniami, 

 which is the most satisfactory, is the following : The serum is diluted by 

 the addition of nine volumes of distilled water, and then carbonic acid 

 gas is passed through till the globulin is precipitated. The precipitate 

 is separated off by the centrifuge, and the clear fluid contains the 

 end-piece, diluted, of course, ten times : The precipitate, containing the 

 mid-piece, is dissolved in '8 per cent, sodium chloride solution, a con- 



