WHAT IS DISEASE ? 251 



period of life e.g. the breaking down of tissue in a chrysalid 

 may be a disease at another period ; what is normal in one 

 part of the body e.g. proliferation of cells may be a morbid 

 growth in another region. Disease is a relative concept and 

 does not admit of strict definition. 



Our point here is indeed a familiar one, for the tritest~of 

 quotations remind us of the kinship between genius and madness, 

 or of the resemblance between the lunatic, the lover, and the 

 poet. As a matter of fact, Ziegler remarks, genius, talent, and 

 mental derangement do sometimes occur in one family. The 

 useful glutinous threads of mucus with which the male stickleback 

 fastens together his nest of seaweed are remarkable renal secre- 

 tions which, if we did not know their utility, would almost 

 certainly be regarded as the symptoms of a kidney disease. 

 Whether we take the changes in the adult salmon when 

 fasting in freshwater, or the dissolution of the blowfly's maggot 

 as it passes into the pupa state, or the condition of the tadpole 

 as it loses its tail and becomes a miniature frog, or the necrosis 

 at the base of a stag's antlers before they fall off, we have to 

 deal with processes which, though now normal occurrences in 

 the cases cited, would in other cases spell disease. 



A great authority puts the point tersely : " Disease is a 

 state of a living organism, a balance of function more unstable 

 than that which we call ' health ' ; its causes may be imported, 

 or the system may ' rock ' from some implicit defect, but 

 the disease itself is- a perturbation which contains no elements 

 essentially different from those of health, but elements pre- 

 sented in a different and less useful order " (T. Clifford Allbutt, 

 System of Medicine, 1896, vol. i. p. xxxii). 



Optimism of Pathology. It does not seem possible to find 

 any criterion which will serve in all cases to differentiate a 

 new variation making for increased efficiency from another 

 which makes for disease. Experience lends security to the 

 judgment of the physician or the breeder in a large number of 



