964 THE ANIMAL VIRUSES 



precipitins have been demonstrated more frequently than agglutinins or comple- 

 ment-fixing bodies. 



Recent work, particularly with vaccinia, has revealed an antigenic complexity 

 in the viruses similar to that present in many bacteria. The elementary bodies of 

 vaccinia appear to contain two agglutinogens, one of which, L, is destroyed by 

 exposure to 56° C. for one hour, the other of which, S, withstands a temperature of 

 at least 95° C. for this time. By suitable methods precipitinogens can be extracted 

 from infected material and from tissue cultures which appear to correspond to the 

 agglutinogens in the elementary bodies (Craigie 1932, 1935, Smith 1932, Craigie 

 and Wishart 1934a, b, 1936, Ch'en 1934, Salaman 1934, Parker and Rivers 1937, 

 Smadel et al. 1940a). It was thought at first that the two antigens were quite 

 separate, and that the heat-stable precipitinogen was a polysaccharide hapten ; 

 but more recent work has shown that both the L and the S substances are con- 

 tained in a single protein molecule (Shedlovsky and Smadel 1942, Shedlovsky et al. 

 1943, Smadel et al. 1943). In addition, two further antigens have been demon- 

 strated in vaccinial elementary bodies. One is the so-called NP or nucleoprotein 

 antigen described by Smadel, Rivers and Hoagland (1942), and demonstrable 

 by precipitation. The other is the- X antigen, which can be demonstrated by 

 agglutination, using a serum from which the LS and NP antibodies have been 

 removed by absorption (Craigie and Wishart 1936, 1938, Smadel et al. 1942). 

 Soluble antigens, capable of reacting in complement-fixation or precipitin tests, 

 have been demonstrated in other viruses, such as the viruses of lymphocytic 

 choriomeningitis and lymphogranuloma. 



A further analogy with bacteria is afforded by the demonstration of multiple 

 antigenic types in a single species of virus. For example, at least three distinct 

 types of foot-and-mouth virus, differing in their infectivity, ha^e been found 

 (Vallee and Carre 1922, Waldmann and Trautwein 1926). Several immuno- 

 logically distinct types of poliomyelitis have now been differentiated ; some of 

 these are so sharply defined that the serum of monkeys convalescent from infection 

 with one type will not protect against another (see Sabin 1941). 



The existence of a group antigenic relationship such as that demonstrated 

 between the viruses of influenza and swine influenza (see Chapter 74) is again 

 reminiscent of the antigenic morphology of bacteria. 



The inoculation of many viruses into suitable animals is followed by the appear- 

 ance of neutralizing antibodies in the serum. The mode of action of these anti- 

 bodies forms a constant subject of discussion. Whether they destroy the virus, 

 whether they merely inactivate it, whether they sensitize it, or whether they fail 

 even to combine with it, is still not known with certainty. Most of the evidence 

 seems to be in favour of the occurrence of a slow union between virus and antibody 

 leading to sensitization or actual destruction (see Chapter 55). 



The type of antibody called forth by different viruses varies. The only anti- 

 body to poliomyelitis virus of which we have knowledge is a neutralizing antibody. 

 On the other hand, vaccinia virus stimulates the production of agglutinins, pre- 

 cipitins, and complement-fixing bodies as well as neutralizing antibodies. In 

 some instances, as in the vaccinia and lymphocytic choriomeningitis viruses, the 

 neutralizing antibodies appear to be distinct from the other antibodies (Salaman 

 1937, Smadel et al. 19406) ; and we are still ignorant of the nature of the antigen 

 against which the neutralizing antibody is active. In general, neutralizing anti- 

 bodies are of most help in revealing antigenic affinities and differences between 



