PROPERTIES OF ANTIBACTERIAL SERUM 535 



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

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

 c.'iitrifugp, 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. Sachs and Altmann have 

 introduced the following method : To *5 c.c. of fresh guinea-pig's serum 

 is added 4'1 c.c. of a 75753^ normal solution of hydrochloric acid in 

 distilled water. The sediment is centrifuged off after the mixture has 

 been allowed to stand at room temperature for an hour, and, after being 

 washed, is made up with a suitable amount of distilled water. The 

 separated fluid is neutralised and made isotonic with '4 c.c. of a sV- 3 V 

 normal soda solution containing 10 per cent, sodium chloride. 



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

 case of certain organisms 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. 128-131. 



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 

 becomes diminished and may be practically annulled. This 

 result, which is generally known as the Neisser-Wechsberg 

 phenomenon, has been the subject of much controversy, and 

 cannot yet be said to be satisfactorily explained. It would 

 accordingly be out of place to discuss here the different views 



