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Mr. G. F. Dowdeswell. 



In the asserted discoveries of a microbe in the tissues of the 

 cerebro-spinal system, since the publication of M. Pasteur's statement 

 that this is the seat of the virus, in some instances these have obviously 

 resulted from mistaking the morphological elements of these tissues 

 for micro-organisms. In the case of the statements of M. Fol,* that 

 he has found a microbe in the ganglion cells, and within Schwann's 

 sheath of the nerve fibres, of the encephalon and spinal cord, though 

 these have received the qualified support of M. Pasteur, I have no 

 doubt that the appearances which he describes as microbes are due 

 to alterations in the cells and nerve fibres, produced by the strange 

 modifications of the method of Weigert which he has adopted for 

 preservation and staining. The appearances of stained granules which 

 he describes, can always be produced by methods similar to those he 

 has employed. I may add, that in very numerous experiments, by 

 inoculating from infective medulla the material in which he asserted 

 that he cultivated the microbe, viz., infusion of sheep's brain, I have 

 never obtained the development of any form of vegetation whatever. 



I have myself, as previously stated (' Lancet,' 1886, vol. 1, p. 1112), 

 found a micrococcus in the cerebro-spinal tissues in some cases of 

 rabies. It occurs chiefly in and around the central canal of the 

 medulla spinalis and oblongata, and in the perivascular and peri- 

 cellular lymph channels, but it is exceedingly difficult to stain, and I 

 have not discovered any reagent by which this can be done with 

 certainty, for I found in sections in which it was undoubtedly present 

 — from their being portions contiguous to others in which it was 

 demonstrated in vast numbers — that it was impossible to recognise it 

 by any means whatever, with the best microscopical appliances, and 

 though mounted in media of widely different refractive indices. 



I have not been able to cultivate it constantly, but I did obtain 

 some growths in agar-agar bouillon peptone, though never in any fluid 

 medium, and from the second series of cultivations of these, with a 

 minute portion of its scanty development, I inoculated one rabbit 

 subcutaneously. The animal was unaffected for three months. It was 

 then re-inoculated intracranial ly with a portion of medulla of intensi- 

 fied virulence ; here also it remained unaffected for upwards of two 

 months, when, being again inoculated, it died on the second or third 

 day from accidental causes. 



This, which up to that time was the only case I had had of the 

 failure of infection after intracranial inoculation in upwards of sixty 

 cases, could not have been merely accidental, and was presumably due 

 to a protective or inhibitory action of the cultivation ; but, as I have 

 not been able to demonstrate the presence of or cultivate the microbe 

 constantly, a final conclusion upon its functions must await further 

 observations. 



* ' Archives Sci. Phys. Nat.,' vol. 10, 188(5, p. 327. 



