The President's Address. By the Rev. W. H. Dallinger. 181 



morphological difference between the ordinary septic form and the 

 form that is pathogenic is by no means striking. 



Yet the one is innocuous, the other deadly. The one is an 

 organism with the power of growing enormously in simple chemical 

 fluids containing nitrogenous compounds, such as tartrate of 

 ammonia. The other refuses wholly to grow and multiply in this, 

 but requires more complex compounds, as the proteids, for its nur- 

 ture. Hence it is found in the blood or tissues of man and animals, 

 and becomes a veritable virus. 



The difference, however acquired, is functional immensely more 

 than morphological. And the probable relation between the two 

 forms is one of the most important by-problems of modern biology. 

 It seems on the surface at least that we have here evidence of the 

 operation of the great secular processes of the Darwinian law bring- 

 ing about, in forms that retain a general morphological resemblance, 

 a distinct physiological specificity. 



I grant fully that no direct evidence, by experiment, of the 

 change has been yet given us. 



It is true that from the close general resemblance between 

 Bacillus subtilis and Bacillus anthracis it was held that the only 

 difference between them was physiological. This is in all proba- 

 bihty not strictly accurate. But there is something yet to be 

 learned in relation to the life-history of both forms, and certairdy 

 in relation to their mutability. Now Hans Buchner tells us * that 

 he did by successive cultivations of the Bacillus anthracis under the 

 influence of continued alterations of the nutrition, see it gradually 

 change into the Bacillus subtilis ; that in fact this deadly form by 

 being passed through successive cultures at a temperature of from 

 35° to 37° Centigrade loses its pathogenic qualities, becomes, in 

 short, bereft of its specific physiological character. 



But more striking yet is the affirmation made by the same 

 savant, that he has changed the harmless Bacillus subtilis into the 

 deadly B. anthracis by similar processes. 



To one who has fully comprehended the meaning and the 

 operation of the Darwinian law, it will be at once apparent that 

 there must be error somewhere in this matter. 



If the law of actual variation, "with all that is involved in 

 survival of the fittest, could be so readily brought into complete 

 operation, and yield so pronounced a result, where would be the 

 stability of the organic world? Nothing would be at one stay. 

 There could be no permanence in anything living. 



_ This immediately impressed me nearly four years ago on reading 

 this remarkable paper, and there can be no shadow of doubt that 



* " Ueber die experimentelle Erzeugung des Milz-brand-contagiums aus den 

 Heupilzen." SB. Math. Piiys. Classen K. Bayer. Akademie d, Wiss., 1880, 

 Heft iii. 



