C INCEPTION OF IMMUNITY 3 



immunity. Unreliable and erroneous results are the inevitable out- 

 comes of such unscientific work. 



The plan followed in this book consists in taking up all of the important 

 principles and methods of immunity, even though at present some may 

 attract no direct practical attention. The principle of the now widely 

 important Wassermann reaction had been described years previously by 

 Bordet and Gengou, but merely from a purely theoretical standpoint. 

 Only with the development of the Wassermann test did it attain its prac- 

 tical importance. 



To start systematically, it is necessary, primarily, to under- 

 Conception stand certain terms frequently employed. First, the word 

 of Immunity, immunity requires explanation: 



After an individual has recovered from an infectious disease, 

 he passes into a state where he is less or even not at all susceptible to the 

 same infection, although no macroscopical, microscopical or chemical 

 change can be shown to have taken place in his system. This condition is 

 one of immunity. And as the body itself by its own struggle with the 

 invading bacteria has brought about this immunity, it is known as " active 

 immunity." Jenner and Pasteur have employed this mode of immunity 

 acquired spontaneously by overcoming an infection in their principle 

 of prophylactic vaccination. The exact nature of this active immunity 

 is only partially understood. It can be shown, however, that the indi- 

 viduals thus actively immunized have within their organism reaction 

 bodies of a specific nature directed against the infecting elements and 

 their poisonous products. These reaction bodies, which circulate mainly 

 in the blood serum, are known as Antibodies. 



The antibodies are of differert classes depending entirely upon their 

 varied forms of activity. While some, such as the agglutinins and pre- 

 cipitins, have the property of grouping their respective invading agents 

 into small clumps or precipitates, without at the same time embracing 

 protective powers, there are other antibodies which act essentially for 

 the defence of the organism. They attain this by neutralizing the 

 poison of the bacteria (antitoxins) or by destroying the bacteria (bacteri- 

 olysins), or so altering the bacteria that the latter can be more easily 

 destroyed by the cells (bacteriotropins, opsonins). The last three types 

 of immunity can be designated respectively, as antitoxic, bactericidal,, 

 and cellular immunity. Naturally there are many intermediate forms. 

 It is very probable that besides these well-recognized forms of immunity 

 there may be others, still unknown. Cellular immunity must surely have 

 a far greater range of importance than is at present ascribed to it. There 

 is, no doubt, a distinct cell immunity which acts without the aid of any 

 serum substance and is known as "Tissue Immunity" ("histogene" 

 Immunitat) . 



