19] i] Smith, Self-Multilation in Cryptobranchus. 65 



side was healthy living tissue, on the other tissue which seemed 

 insensitive, since the animal did not respond when the affected 

 regions were stimulated with forceps. 



On March 15, 1910, the digits of one hind foot had been 

 entirely cast off. and the wound had begun to heal over. The 

 other hind foot had lost the integument and flesh of the first 

 phalanges, and the latter projected as naked bones. The posterior 

 two inches of the tail were still connected with the body by the 

 vertebral column. 



About March 30, the infected portion of the tail dropped off, 

 one vertebra being left bare with conspicuously projecting 

 transverse processes. 



About three months later (July 7) it was observed that the 

 stumps of the tail and hind feet had entirely healed over, so that 

 the bones were no longer exposed. No signs of infection were 

 visible on any part of the body of the animal. That it had quite 

 recovered its vitality is evidenced by the fact that while handling 

 it I received a bite on the fingers sufficient to draw blood — the 

 only time I have ever been bitten by a hellbender. 



About a month later the animal died, apparently from a fresh 

 attack of the nitrogen disease, so that I was unable to observe to 

 what extent regeneration might take place. 



The sloughing off of injured or infected tissue is not uncom- 

 mon in vertebrates but in such cases the tissue is usually gotten 

 rid of piecemeal. In the case described in Cryptobranchus the 

 affected portions remained intact until dropped off entire, and 

 this was accomplished by a break in the tissue bordering the 

 reeion of infection. When we remember that the skin of Crypto- 



• 



bra 11 chits is tough and flexible, almost as far removed from being 

 brittle as it is possible to imagine, we find it impossible to explain 

 its breaking at this point as due to purely mechanical factors. 

 Pathological changes in the tissues, proceeding in advance of the 

 actual infection, must so alter their physical properties that a 

 break occurs in precisely the region that is most advantageous to 

 the animal in getting rid of the infection. 



Zoological Laboratory, University of Wisconsin. 



January, 1911. 



