ULTRA-MICROSCOPIC OR FILTERABLE VIRUSES 265 



tissue in the tube. Microscopic examination of this opalescent 

 matter, especially by dark-field illumination, reveals the pres- 

 ence of coccoid bodies conspicuous for their variation in size. 



Their true nature has not been determined. The disease 

 can be reproduced in monkeys by inoculation with the cul- 

 tures, but not with regularity. 1 



By an analogous method Noguchi has cultivated from 

 both rabies and trachoma bodies that he regards as etiolog- 

 ically related to the diseases from which they were obtained. 

 It is not possible as yet to be either certain as to the accuracy 

 of his suspicions or to satisfactorily classify the bodies found 

 in his cultures. In some respects they suggest bacteria, in 

 some protozoa and taking them in conjunction with the 

 tissue findings in the diseases it seems fair to suspect that 

 they may be developmental forms of the Negri bodies con- 

 stantly present in rabies in the one case or the singular cell 

 inclusions common to trachoma, the so-called "trachoma 

 bodies" in the other. 2 



In the study of many of the common diseases, notably 

 the exanthemata, both at autopsy and during life, by the 

 methods above outlined, the investigation often yields 

 negative results, and yet there is every reason for believing 

 these diseases to be dependent for their existence upon 

 invasion of the body by some form or another of living 

 microorganisms, capable of growth in the tissues and sus- 

 ceptible of being transmitted from individual to individual, 

 either directly or indirectly. It is possible that the applica- 

 tion of one or another of the foregoing methods to the 

 study of these diseases may demonstrate that some of them 

 at least are due to the presence of so-called filterable viruses. 



1 For details see Flexner and Noguchi, Jour. Exp. Med., 1913, vol. xviii, 

 No. 4. 



2 For particulars see Noguchi, Jour. Exp. Med., 1913, No. 4; ibid., 1913, 

 No. 5. 



