THE PRESIDENT'S ADDRESS. 187 



modified in its mode of manifestation by the constitutional con- 

 dition of the patients. Now, my own belief is that there is a very 

 large amount of this modification, and that there is a very large 

 range of forms of disease that may be produced by the same infec- 

 tion ; that the bacteria, when cultivated, as it were, in the human 

 body, may undergo a very considerable amount of modification in 

 their potentialities, and that they may under some circumstances 

 give rise to one form, and under other circumstances to another 

 form of disease. I Worked out this view about a year and a half 

 ago in a paper which I published in the " Nineteenth Century," 

 which I daresay is accessible in some library to any of you 

 who care to learn my views upon it. I may say that 

 since I have published that paper I have had a very large amount 

 of evidence sent to me kindly by various practitioners in the country, 

 as to the variety of manifestations of what was clearly the same 

 contagion, and these facts all fall in with my general natural history 

 notions, you observe, formed from the experience of a life ; for I 

 may say that whenever I have come across a man who has attended 

 to one particular groove — plants or animals — I have inquired about 

 range, and have always learned it was a great deal wider than books 

 would lead you to suppose — that you may have specific descrip- 

 tions, but that these specific descriptions are liable to very con- 

 siderable modification — I should say the types are liable to very 

 considerable modification. Now this is a very important considera- 

 tion, and 1 may say that there Professor Ray Lankester has per- 

 formed good service in the careful study that he made some years 

 ago of the form of these bacilli. That study is contained in the 

 i( Microscopical Journal " — not the " Journal of the Microscopical 

 Society," but the u Quarterly Microscopical Journal " — and I believe 

 that the varieties that he described in that — the variation of form — 

 have been quite confirmed by many who have made a special study 

 of bacilli. To my mind the variation of form and the variation of 

 potentiality constitute one of the most interesting subjects of bio- 

 logical inquiry at the present time; and there is just one other very 

 curious point in which microscopical evidence is wanting to complete 

 a most interesting scientific research. Many of you know, I have 

 no doubt, that the process of what is called nitrification, or the pro- 

 duction of nitric acid, has long been one of the problems of che- 

 mistry. Of course w r e all know that nitric acid can be produced by 

 passing a succession of electric sparks through a mixture of nitro- 



