558 Sir John Rose Bradford [May 30, 



hitherto known is the reputed cause of influenza, the bacilkis of 

 Pfeiffer ; this is said to be 1 • 5 />t long and ' 3 /x in diameter. It 

 will be seen from this comparison that only the largest of the filter- 

 passing organisms may reach as a maximum size the diameter or 

 breadth of the average bacillus, and that some of the smallest — 

 e.g. those of influenza and of rabies — are roughly one-tenth of the 

 length of such a small organism as the bacillus of Pfeiffer. This 

 comparison perhaps gives a better idea of the extreme smallness of 

 these filter-passing organisms. 



The question naturally arises as to whether these organisms exist 

 in a still smaller form, or even in an ultra-microscopic form. In all 

 •cultures it is possible to see very small forms, so small that they 

 cannot be measured, at any rate at present, and it is of course quite 

 possible that the clearly visible forms are only better grown specimens 

 of the smallest forms. On the other hand, the visible forms are 

 very constant in their morphology in the different diseases, and can 

 ])e recognized in the actual secretions and fluids of the body of the 

 human patient and in the tissues of the experimental animals, as well 

 as in the tissues of fatal human cases. Further, they can be recog- 

 nized in the filtrates through suitable filters. Hence, although it is 

 of course possible that ultra-microscopic forms may exist as a stage 

 in the life-history of the particular organisms causing the diseases 

 now under consideration, yet such a belief is not necessary for the 

 explanation of the facts as they are at present known to us. The 

 organism of influenza or of rabies can be seen in the filtrate obtained 

 by filtering a culture of the virus through a porcelain Massen filter, 

 hence it is not necessary to hypothecate an ultra-microscopic form in 

 order to explain the fact that a living culture can be successfully 

 obtained from such filtrates. 



In rabies the organism has been obtained by direct culture from 

 the brains of animals forwarded to us, in which rabies had been 

 produced by inoculation in the laboratory. All the results therefore 

 were obtained from laboratory animals proved by others to have died 

 from rabies. This material was derived from both English and 

 French sources, in the former from the recent outbreak in this 

 country, in the latter the virus fixe of the Pasteur Institute. We 

 have as yet had no opportunity of making direct observations on 

 the disease as it occurs in nature. In the other five diseases the 

 respective organisms have been isolated clinically by culture from the 

 blood of patients during the febrile periods of the maladies, and it is 

 of some interest that this blood culture should be successful not only 

 in maladies like trench fever and influenza, where fever is a marked 

 feature of the illness, but also in nephritis, encephalitis and poly- 

 neuritis, where fever is often only slight in amount and is liable to 

 occur only in the initial stages of the disease. Although the febrile 

 period of these diseases is that most suitable for the recovery of the 

 organism from the blood, yet in several of these maladies it is possible 



