550 Sir John Rose Bradford [May 30, 



WEEKLY EVENING MEETING, 

 Friday, May 30, 1919. 



Sir James Crichton-Beowne, J.P. M.D. LL.D. D.Sc. F.R.S., 

 Treasurer and Yice-President, in the Chair. 



Sir John Kose Bradford, K.C.M.G. C.B. M.D. D.Sc. F.R.S., 

 Late Consulting Physician to the British Expeditionary Force. 



A Filter-passing Virus in Certain Diseases. 



The term virus is applied by pathologists to a living agent that is 

 proved to be the actual cause of any given disease, and the progress 

 of knowledge tends slowly but surely ever to increase the number of 

 diseases in which such a definite cause is estabHshed as the essential 

 factor in their production. In many, perhaps in all, diseases more 

 than one factor is necessary, thus so-called predisposing causes may 

 not only always be necessary, but may sometimes be of more 

 immediate practical importance than the presence of the actual 

 virus. Measures directed to control the ill-effects of predisposing 

 causes may be of more avail in controlling disease than measures 

 directed to destroying the actual cause or virus. Nevertheless, the 

 study of the actual cause of disease remains of paramount interest 

 and importance, inasmuch as the satisfactory study, and therefore 

 the satisfactory control, of disease is impossible until we know its 

 cause with certainty. Unless we can diagnose disease with absolute 

 certainty, and not merely as a matter of opinion, the position is 

 unsatisfactory. In many instances diagnosis in the real and strict 

 sense of the word is impossible when the cause of the malady is 

 unknown. With the discovery of the cause, methods of diagnosis 

 of extreme accuracy can frequently be devised, and then a malady 

 can be recognised with certainty. Further, such discoveries often 

 lead to the recognition of other facts of importance, and slighter 

 forms of the disease in question, previously either not recognised at 

 all, or else mistakenly regarded as belonging to some other group, 

 are detected. This is often a point of great practical importance, 

 as is also the somewhat similar fact of the discovery of what are 

 known as "carriers" — i.e. individuals not themselves ill, but never- 

 theless harbouring and capable of conveying to others the infection, 

 it may be, of some virulent and dangerous disease. All these facts 

 depend upon the discovery and recognition of the specific virus or 

 cause of the disease in question, and remain unknown until this 

 specific virus is isolated and proved to be the true cause of the 



