34 



patches of hair. But in birds the peculiar characteristic of the incomplete 

 form is the symmetrical arrangement of the white plumage. This alone, 

 though strongly in favour of disease as a cause, would quite destroy any 

 parasite theory. Agaiu, turning to the possibility of other diseases, 

 Erasmus Wilson has pointed out that certain nervous afFectious produced 

 patches of baldness often symmetrical in human beings. Patches of grey 

 and white hair in the eyebrows and hair on the face are occasionally seen 

 in cases of severe neuralgia. Here, then, are examples of trophic dis- 

 turbances in the appendages of the skin following on obscure nervous 

 changes. Whether the incomplete form in birds may be due to similar 

 causes or not remains to be proved ; all that can be said is that the 

 posssibility is not unlikely. From nervous disease it is ouly oue step to 

 those phenomena due to what is known as correlation, a long name given 

 to a physiological connection between two organs, a connection which we 

 do not understand. If certain organs in the human body become diseased 

 the skin becomes pigmented, producing an affection known as "black 

 jaundice." Here is an example of a correlation — an obscure connection 

 between these organs and the skin, in consequence of which if one organ 

 be diseased the other exhibits morbid changes also. Other instances may 

 be quoted, among which perhaps the most striking is the blue-eyed white 

 cat, which, according to Darwin and Tait, is always deaf. The latter 

 authority also states that this peculiarity is confined to males. These 

 instances point rather to the probability of the incomplete form being a 

 result of disease ; and when it is considered how difficult it is to associate 

 the incomplete form with any other cause, the argument for disease is 

 further strengthened. In support of the argument, Mr. Hall pointed out 

 that age, food, cross-breeding, though commonly mentioned as likely 

 causes, cannot be considered as such. He also showed that though the 

 complete form may be hereditary, the incomplete is not so. This, again, 

 favours the argument that the latter is a result of disease, and is not a 

 congenital peculiarity. 



Mr. M. J. Oliver pointed out that Mr. Hall's paper was of great 

 interest, the subject not appearing hitherto to have been much studied ; 

 and secondly, because it was of interest not only to naturalists, but also to 

 physiologists and pathologists. He considered that Mr. Hall, in confining 

 himself to albino birds, increased the difficulty of finding a cause for a 

 condition which occurred in various orders, and was widely distributed in 

 nature. 



Mr. Hall stated on Darwin's authority that albino birds have never 

 been seen to pair in the wild state, but do so when domesticated. 

 Referring to this fact it is stated by Wallace that our domestic breeds of 

 white animals, e.g., mice, rats, cats, pigeons, ducks, &c., were probably 

 derived from albino specimens, which on account of their rarity were 

 preserved and bred from by man. And in the case of species inhabiting 

 Alpine or Arctic regions were preserved by the white colour proving a 

 protection, affording concealment in the snow. 



