

PROPHYLACTIC SERUMS 223 



According to Metchnikoff the bactericidal substances in the serum are derived 

 from the leucocytes : some (immune bodies, amboceptors, or sensibilisatrices) are 

 elaborated in the leucocytes and excreted into the plasma as they are formed, whence 

 they pass into the different tissues of the animal ; the others (complement, cytase 

 or alexin) are also of leucocytic origin but are only set free on the death and dis- 

 integration of the leucocytes. Petterson and Schneider consider that there are 

 yet other substances in the leucocytes capable of destroying micro-organisms (endo- 

 lysins, leukins). 



In the majority of cases the bactericidal substances of the serum of im- 

 munized animals intervene to prepare the micro-organisms for the action of 

 the leucocytes and facilitate their ingestion and destruction (vide opsonins). 



In immunized animals therefore over and above the phagocytic reaction 

 there exist in the fluid part of the blood (serum) certain substances of great 

 importance which play a prominent part in the phenomena of immunity. 

 The properties of these immune serums will be now studied a little more fully. 



The serums of immunized animals may exhibit one or more or all of the 

 following properties each quite independently of the other and in different 

 degrees. 



1. Prophylactic and therapeutic properties. 



2. Antitoxic properties. 



3. Agglutinating properties. 



4. Bactericidal properties. 



5. The property of preparing micro-organisms for ingestion by the leuco- 

 cytes. This property which is due to the presence of special substances, 

 opsonins, would appear to be connected with the bactericidal properties. 



SECTION I. PROPHYLACTIC AND THERAPEUTIC SERUMS. 



It has already been pointed out that the serum of an animal vaccinated 

 against a micro-organism if inoculated into a fresh animal confers on the 

 latter an immunity of short duration. 



This passive immunization is absolutely specific and is only exhibited 

 towards the species of organism with which the first animal was vaccinated. 



The serum of an animal vaccinated with toxin if inoculated into a fresh 

 animal confers on the latter an immunity against the same toxin and also 

 against the micro-organism which elaborated the toxin. 



Example. If a normal guinea-pig be inoculated with antidiphtheria serum it is 

 protected against the inoculation of diphtheria toxin and also against inoculation 

 with the diphtheria bacillus. 



On the other hand, if an animal be vaccinated with micro-organisms its 

 serum has no protective action against the toxin of the organism though 

 it protects against the organism itself. 



Example. The serum of an animal vaccinated with the cholera vibrio (vide 

 Cholera) will protect a normal animal against an inoculation of the vibrio. A 

 trace of the serum, for instance, inoculated into a normal guinea-pig will vaccinate 

 the latter against choleraic peritonitis. On the other hand the serum affords no 

 protection against an inoculation of the toxin and is totally ineffective in intestinal 

 cholera which is an intoxication (Metchnikoff). 



In all of the foregoing cases the serum acts as a prophylactic ; that is to 

 say, it immunizes the animal to which it is administered provided it be inocu- 

 lated before or at the same time as the organisms or toxin. 



Some serums exhibit therapeutic as well as prophylactic properties. If 

 inoculated after the infection, even though the first symptoms of infection 

 have appeared, they abort the disease and lead to recovery. The curative 



