PROPEKTIES OF ANTIBACTERIAL SERUM 573 



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 0° 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 serum should also be used as fresh as possible after the blood is withdrawn 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 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 p. 127. 



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 %vill 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 

 with regard to it. (Regarding some theoretical considerations 

 as to the therapeutic applications of antibacterial sera, vide 

 p. 584.) 



The laws of lysogenesis are, however, not peculiar to the 

 case of solution of bacteria by the fluids of the body, but hold 

 also in the case of other organised substances, red corpuscles, 

 leucocytes, etc., when these are introduced into the tissues of an 

 animal as in a process of immunisation. Of such sera the 

 hemolytic have been most fully studied, and, owing to the 



