862 BIOLOGICAL TRAINING AND STUDIES. 



poison varies in direct ratio to the quantity imbibed or infused, just 

 as though it were so much alcohol, or so much alcoholic tincture of 

 musk or cantharides ; or secondly, that its potency varies in direct 

 ratio to another varying standard, viz. the size of the animal pro- 

 ducing it. Now the vaccine matter from the arm of a child is as 

 potent as the vaccine matter from the arm of any giant would be ; 

 and whether a grain or a gramme of it be used will make no differ- 

 ence, so long as it be used rightly. There is a contrast, indeed, 

 between the modus operandi of these two animal poisons. I would 

 add that in the ' Edinburgh Monthly Medical Journal ' for the 

 present month there is a very valuable paper^ one of a series of 

 papers, indeed, of the like character, by Dr. Fayrer, where at 

 page 247, among much of anatomical and other interest, I find the 

 following important statement : ' This poison may be diluted with 

 water, or even ammonia or alcohol, without destroying its deadly 

 properties. It may be kept for months or years, dried between 

 slips of glass, and still retain its virulence. It is capable of ab- 

 sorption through delicate membranes, and therefore it cannot be 

 applied to any mucous surfaces, though no doubt its virulence is 

 much diminished by endosmosis ^. It appears to act by a catalytic 

 form ; that is, it kills by some occult influence on the nerve 

 centres.' There is such a thing as an ignorance which is wiser 

 than knowledge, /br the time, of course, only ; such an ignorance is 

 wisely confessed to in these words of Dr. Fayrer's. An explanation 

 may be true for some, yet not thereby necessarily for all, the facts 

 within even a single sphere of study; even a true explanation may 

 have but a very limited application, as a tangent cannot touch 

 a circle at more than a single point. The memoirs published in 

 our own reports by Dr. B. W. Richardson, on the action of the 

 nitrites, and those published by Dr. A. Crum Brown and Dr. T. R. 

 Fraser, there and elsewhere, on the connexion between chemical con- 

 stitution and physiological action, deserve especial study as bearing 

 on the other side of this discussion ; whilst Professor Lister's papers 

 show how the reference of certain diseases to vitalistic agencies 

 may become of most vital importance in practice. There exists, as 

 is well known, a tendency to resolve all physiological into physico- 

 chemical phenomena : undoubtedly many have been, and some more 



^ Diapedesis may account for what virulence remains, and the poison may therefore 

 possibly be a cytoid. 



