7-1 ANALOGY OF DISEASE. [IXTROD. 



Species arise through discontinuous transition from one state of 

 iii.-.-l, :l i,i,-;il or chemical stability to another state of stability, there 

 M.-V, -rtheless remain large classes of discontinuous variations, and 



- .-it'ii.' Differences still more, whose Discontinuity bears no 

 Malogy with these. To these phenomena inorganic Nature 



ra IK. parallel. We may see that they are discontinuous and 

 tint tin-it- course is in some way controlled, but as to the nature 

 of this control we can make no guess. 



Though the resemblance may be misleading, it is neverthe- 

 less true that in living Nature there are other phenomena, those 

 which present a Discontinuity closely comparable with 

 tint of nianv variations. In problems of disease we meet again 

 tin- >ame problem which we meet in Variation, namely, changes 

 whi.-h may be complete or specific, though occurring so suddenly 

 \clmle the hypothesis that Selection has been the limiting 

 cause. All this is" familiar to everyone who has considered the 

 |n-< .Kit -in of Species. 



For though, like discontinuous variations, the manifestations 

 ..t' -p--eiiic disease are not always identical, but differ in intensity 

 ami d' arying about a normal form, still these manifestations 



inav b.- -p--citic iu the sense in which the term is used with reference 

 to the rharai-t'Ts of Species. If we exclude those diseases whose 

 -p'-ejtie characters are now known to be the result of the invasion 

 . .t' -p.-citic or^ani-ms, there still remain very many which are known 

 and rece,_rni/ed lv definite and specific symptoms produced in the 

 l>"dv. though thne is as yet no evidence that they are due to 

 specific organisms. [Of cour.-e it' it were shewn that these diseases 

 also result from tin- action of specific organisms, they then only 

 pre-.-nt to H- aijain tin- original problem of Species ; for if the 

 iie-- or Specie-, of a disease is due to the definiteness, or 

 . ,,f th.- micro-organism which causes it, the cause of that 

 of the 1 1 1 ji To-or^ai iisi ii remains to be sought, and we 

 are -imply left with a particular case of the general problem of 

 Specie-.) Mut in the meantiuir we can see that the manifestations 

 specific : ami while \v do not know that they result from causes 

 themselves -pe-'jtic, the nature of the control in obedience to which 

 tip -pecitic is unknown. 



The parallel between disease and Variation may be mis- 

 leading, l.ut this much at leasl may fairly be learned from it: 

 that the -y-t,-m of an organixed being is such that the result 

 of its disturbance may lie specific. And in the end it may well 

 be that the prolilem of Species will be solved by the study of 

 pathology: tor the likene-,-, between Variation and disease goes 

 far to Mipptu-t th.- view which Yirchow has forcibly expressed, 

 that " every deviation from the type of the parent animal must 

 have it-, foundation on a path .logical accident 1 ." 



1 11. Vn:. llu\v, Ji.iirn-il </ l'ittl<i>l'>;iy, I. 1892, p. 1'2. 



