INFECTIOUS DISEASES OF MICE 405 



serial intranasal passage of suspensions of mouse lung. Seven distinct 

 strains, termed Li to L7 in accordance with Kliencberger's nomenclature, 

 have been isolated in England, four of which were found in mice. Similarly, 

 five separate types, A, B, C, D, and E of Sabin (227, 230), have been dis- 

 covered in laboratory mice in America. Illness produced by these agents 

 is important in that it may appear in animals inoculated with other materials 

 and must therefore be recognized. Since the organisms are natural 

 inhabitants of mice, it is probable that under certain conditions they may 

 incite spontaneous disease. 



The experimental disease. — The type of experimental disease produced 

 in mice varies with the strain employed and with the route of inoculation. 

 The most striking illness results from intracerebral injection of the L5 or 

 Type A strain, isolated originally from mice which developed "rolling dis- 

 ease" following inoculation with the viruses of yellow fever or lymphocytic 

 choriomeningitis (70) or with the toxoplasma (224). After an incubation 

 period of 2 or 3 days — occasionally as long as 10 days — signs of illness 

 appear. Some of the animals show little beyond roughening of the fur and 

 irritability; others show a variety of nervous signs and symptoms, often 

 choreiform in type. Characteristically, many afflicted animals turn in 

 circles with their tails as a fixed axis. 



According to Findlay et al. (70), approximately 10 per cent of the animals 

 showed the "rolling" phenomenon; the head was rotated slowly, the foreleg 

 raised from the ground, and with a jerk the animal rolled over in one direc- 

 tion for fifty or more revolutions. Death usually followed within 24 hours 

 after rolling began. Three-fourths of the animals died in 2 to 7 days, and 

 of the one-fourth surviving, about half developed acute hydrocephalus i to 

 2 weeks later. No attempt was made to separate the virus of lymphocytic 

 choriomeningitis from the L5 organisms, but it was found that other strains 

 of pleuropneumonia-like organisms mixed with the virus did not produce 

 the disease. Interestingly enough, animals which survived did not show 

 symptoms of choriomeningitis and were no longer susceptible to that virus — 

 possibly another instance of the "interference phenomenon" (218). Patho- 

 logically, an intense inflammatory reaction with polymorphonuclear infil- 

 tration was found in the substance of the cerebral cortex, the floor of the 

 lateral ventricles, the choroid plexus, and the meninges, frequently resem- 

 bling acute abscesses. In cases of hydrocephalus, the ventricles were 

 markedly dilated with a corresponding decrease in thickness of the cortex. 

 Smears stained with Giemsa's stain revealed many extracellular and intra- 

 cellular granules approximately twice the size of the elementary bodies of 



