438 BIOLOGY OF THE LABORATORY MOUSE 



vated by o.oi per cent formalin in 48 hours and by a temperature of S5°C. in 

 30 minutes. Studies of the inclusions (18, 98, 144) have revealed the presence 

 of elementary bodies entirely similar to the Paschen bodies of vaccinia and 

 the Borrel bodies of fowlpox. The inclusions are resistant to digestion with 

 trypsin (24). Propagation of the virus has been successful only in tissue 

 culture and on the chorio-allantoic membrane of the egg (56, 57, 199, 40). 



The virus is strikingly species-specific. Only mice show signs of the 

 disease, although inapparent infection has been demonstrated in the rat (39). 

 One attack of the disease confers a solid immunity upon the survivors, in 

 whose serum neutralizing antibodies are demonstrable. Attempts to pro- 

 duce immunity by the use of inactivated virus have thus far been unsuccess- 

 ful (24), and prevention of the disease can be accomplished only by general 

 measures. 



An epidemic disease, somewhat similar to ectromelia, has been reported 

 by Thompson (273, 275). Intracytoplasmic and intranuclear inclusion 

 bodies were found in the parenchymatous cells of the liver, but were absent 

 from epithelial tissues. Further comparison of the two diseases was not 

 reported. 



Lymphocytic choriomeningitis. — The virus of lymphocytic choriomenin- 

 gitis was first obtained from mice by Traub (291, 292) in 1935. It was 

 encountered during his work with the viruses of equine encephalomyelitis 

 and hog cholera and was found to be distinct immunologically and path- 

 ologically from both of them. In spite of the fact that he at first had 

 recognized no disease in his mouse colony, it seemed likely that the mouse 

 was the natural host of the virus. Accordingly, he inoculated a group of 60 

 5-week-old mice with sterile bouillon by the intracerebral route. Nine of 

 these animals developed symptoms in from 3 to 13 days, and 4 died. No 

 bacteria were obtained by culture. Inoculation of suspensions of brain into 

 guinea pigs reproduced the disease. From later studies, he estimated that 

 about 50 per cent of the mice were infected with this agent, which was 

 identified as the virus of lymphocytic choriomeningitis (292, 219, 220). 



The original isolation of the virus was reported in 1934 by Armstrong and 

 Lillie (14), who accidentally encountered it in monkeys during the course of 

 their studies on the epidemic of encephalitis in St. Louis. The origin of this 

 strain was not definitely determined. Subsequently, the virus has been 

 isolated from cases of meningitis in man (219, 246. 69, 138, 15), and from 

 laboratory and house mice (69, 146, 138, 15). The latter observation is of 

 particular interest since the virus was found in grey mice (Mus musculus) 

 trapped in two houses in which human cases occurred (15). Accidental 



