452 BIOLOGY OF THE LABORATORY MOUSE 



The disease may be transmitted to normal adult or young mice by 

 inoculation of emulsions of the infected salivary glands or by filtrates of 

 such emulsions. Negative results are obtained with other tissues. No 

 clinical manifestations occur in adult animals and the virus localizes in the 

 salivary glands regardless of the route of inoculation. Following intra- 

 cerebral injection a mild meningeal reaction may result, with exudation of 

 mononuclear cells and occasional inclusion bodies within cells of the cerebral 

 tissue, endothelial cells of the choroid plexus, and mononuclear cells. In 

 young animals (3 weeks of age) a fatal infection may be produced by intra- 

 peritoneal and occasionally by intracerebral inoculation (168). Death 

 usually occurs in 3 to 7 days. Necrotic lesions are found most extensively 

 in the liver, spleen, adrenals, lymph nodes, and subperitoneal tissue. Intra- 

 nuclear inclusions are frequent in these tissues, but are not found in the 

 salivary glands unless the animal survives for 8 days or longer. Experi- 

 mentally, strains of mice vary in their susceptibility to the virus. Other 

 species of animals are resistant. 



The properties of the transmissible agent have not been fully inves- 

 tigated. It is destroyed by a temperature of 6o°C. for 30 minutes. Filtra- 

 tion through a Berkefeld V filter has been accomplished. 



Inclusion bodies in the liver. — Inclusions in hepatic cells are probably 

 very uncommon since Twort and Twort (299) did not notice them in the 

 course of some 12,000 postmortem examinations. Findlay (68), however, 

 observed acidophilic intranuclear inclusions in the livers of all the mice of 

 one strain (Clacton) obtained from a London dealer. They were not found 

 in the livers of newly born mice. Transmission to a disease-free strain of 

 mice was accomplished by inoculation of an emulsion of infected liver. This 

 observation has been confirmed by Thompson (273, 275), who noted hepatic 

 inclusions in 5 of 25 apparently healthy mice as well as during an epidemic 

 which somewhat resembled ectromelia. 



Factors Influencing the Production of Experimental 

 AND Natural Disease in Mice 



The study of any infectious disease is best carried out in its natural 

 host. For obvious reasons, however, an experimental study of certain dis- 

 eases on such a basis may be impracticable if not impossible, and it is neces- 

 sary to resort to a different species of animal. The disease thus obtained 

 may or may not be similar to the original one, but it will be dependent, as is 

 the natural disease, on at least three important variables: the microbe, the 



