FAMILY BORRELIOTACEAE 



i247 



1931, 2013-2028; Swan, Austral. Jour. 

 Exp. Biol, and Med. Sci., 19, 1941, 113- 

 115. 



Strains and substrains : A strain from 

 cottontail rabbits (Sylvilagus sp.), differ- 

 ing from typical myxoma virus, has been 

 studied extensively under the name 

 fibroma virus. This strain in turn is rec- 

 ognized as consisting of variants and has 

 been investigated as typical (OA) and 

 inflammatory (lA) substrains, antigeni- 

 cally alike but the latter tending to 

 generalize in domestic rabbits. Fibroma 

 virus is not lethal in domestic rabbits as 

 the type strain almost always is; it 

 appears to lack some antigenic constitu- 

 ents, inducing the formation of agglu- 

 tinins that give cross reactions with the 

 type but of neutralizing and complement - 

 fixing antibodies that do not. The fi- 

 broma strain does not generally appear 

 in the blood stream, as myxoma virus 

 does, and is not contagious, at least it 



does not spread spontaneously among 

 domestic rabbits as the myxoma strain 

 does; the manner of its spread in wild 

 rabbits in nature is not known. Its 

 particle size has been calculated as 126 

 to 141 millimicrons by centrifugation, 

 125 to 175 millimicrons by filtration. 

 (Ahlstrom, Jour. Path, and Bact., 4(>, 

 1938, 461-472 ; Andrewes, Jour . Exp. Med., 

 63, 1936, 157-172 ; Hoffstadt and Pilcher, 

 Jour. Inf. Dis., 68, 1941, 67-72; Hurst, 

 Brit. Jour. Exp. Path., 18, 1937, 1-30; 

 Austral. Jour. Exp. Biol, and Med. Sci., 

 16, 1938, 53-64, 205-208; Hyde, Am. Jour. 

 Hyg., 24, 1936, 217-226; Ledingham, 

 Brit. Jour. Exp. Path., 18, 1937,436-449; 

 van Rooyen, ibid., 19, 1938, 156-163; van 

 Rooyen and Rhodes, Cent. f. Bakt., I 

 Abt.,0rig.,U:2, 1938, 149-153 ;Schlesinger 

 and Andrewes, Jour. Hyg., 37, 1937, 

 521-526; Shope, Jour. Exp. Med., 66, 

 1932, 793-822; 63, 1936, 33-41, 43-57, 

 173-178. 



