572 IMMUNITY 



Recent observations show 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 guinea-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 Liefmann, 

 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- 

 venient amount being twice the volume of the original serum. During 

 the process of preparation, and afterwards, the serum and the diluting 

 fluids ought to be chilled to a temperature a little above C. ; the 

 serum should also be used as fresh as possible after the blood is withdrawn 

 from the body. 



The phenomenon of bacteriolysis is, however, only seen in the 

 case of certain organisims when an animal is highly immunised 

 against them ; the typhoid and cholera group are outstanding 

 examples. It is also to be noted that it sometimes is seen in the 

 case of a normal serum (vide Natural Immunity). In other 

 cases the bactericidal effect of a serum may occur without the 

 rapid dissolution characteristic of lysogenesis, though other 

 structural changes may be produced. In still other instances, 

 e.g., the anti-sera to staphylococci, streptococci, plague bacilli, 

 etc., a bactericidal effect may be wanting; nevertheless it may 

 be shown that an immune -body is developed in the process of 

 immunisation. This may be done by observing the increased 

 amount of complement which is fixed through the medium of 

 the anti-serum (immune-body), sensitised red corpuscles being 

 used as the test for the presence of free complement. The 

 method is described on pp. 129-132. 



The all-important action of the immune-body is thus to bring 

 an increased amount of complement into union with bacteria; 

 whether death of the bacteria will result or not will depend 

 ultimately on their sensitiveness to the action of the particular 

 complement. 



It is to be noted that in the case of a bactericidal serum there 

 is an optimum amount of immune-body which gives the greatest 

 bactericidal effect with a given amount of complement. If this 

 amount of immune-body be exceeded, the bactericidal action 



