BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 155 



bition in the proprioceptive system, part of the motor system, and 

 some structures connecting the medulla and cerebellum, occur- 

 ring during growth with scarcely any definite degeneration. 



It is not an easy problem to explain from our specimens what 

 part of the cerebellum or spinal cord may have been primarily 

 interfered with in its growth. Again, it is more difficult to ex- 

 plain why just those neurons are especially affected. William- 

 son ('11) holds the opinion that a tendency for alteration in the 

 peripheral parts of the cord may result from the fact that this 

 area has a poorer blood supply than the central. Pitt says there 

 is an inherited tendency toward general early vascular deteriora- 

 tion in certain cases, while Gowers suggests that abiotrophy, or 

 an inherited tendency toward early death of the nerve fibers may 

 occur in this condition (Turner, '10). Though these explana- 

 tions have been given to account for the changes observed in 

 hereditary ataxy, none quite fit in with our cases. The apparent 

 scantiness of the blood-vessels and the capillaries in the cerebel- 

 lar cortex and in the spinal cord in our cases might possibly have 

 some relation to this question, yet this condition of the vessels 

 is far from sufficient to explain all. We are, therefore, as yet 

 entirely ignorant as to why just these systems should be picked 

 out. 



The question then arises as to how these symptoms could de- 

 velop without any degenerative or regressive processes. Since 

 certain groups of neurons in the central nervous system are im- 

 properly developed while others are almost normally developed, 

 there results an unbalanced arrangement in their functions in 

 the early life of the bird which may appear as a disturbance of 

 coordination. In this, our cases seem to be similar to some ex- 

 tent, but not quite the same as the case of Nonne ('05), who re- 

 ported a congenital small central nervous system in the human 

 without degeneration, associated with cerebellar symptoms which 

 Holmes ('07, '07 a) classified as his sixth type of hereditary 

 ataxia from the standpoint of pathologic anatomy. The fact 

 that the original ataxic pigeon no. 151, according to the record 

 (Riddle), recovered from the disturbance when an adult, seems 

 to me to give a sort of confirmation to the above view. 



