BRAINS AND SPINAL CORDS IN ATAXIC PIGEONS 137 



to two-thirds or even one-third of the normal and often shows 

 an irregular breadth, so that it forms a wave-like layer. Measure- 

 ments of this layer here vary from 0.150 to 0.251 mm. in affected 

 and 0.167 to 0.418 mm. or sometimes even to 0.501 mm. in the 

 normal. The granule cells reveal no changes save in some 

 cases they seem to be rather loosely arranged. The Purkinje 

 cells here, though they have generally almost the same appear- 

 ance as in the normal specimen, yet show a slight difference. 

 They are 26.5 to 29.4 ix long and 14.7 to 17.6 mm. wide in the 

 normal on the average, but in the affected birds they are usually 

 a little smaller and slender in shape. In pigeon no. K207 they 

 are 20,5 to 26.5 M in length and 11.8 to 14.7 M in width. The 

 processes or dendrites of the Purkinje cells which run perpen- 

 dicularly to the surface of the cortex, having a measurable 

 length of about 58.8 to 73.5 /x in the normal specimens, while 

 they are short and very often difficult to make out in the affected 

 birds. 



In the sections which were cut horizontally, we can see that 

 the affected birds have not only a narrow molecular layer, but 

 also shallow sulci, and consequently the depth of the gyri is 

 often reduced to one-half to two-thirds of the normal. In 

 addition to this, when sections were being cut it could be observed 

 that in the affected specimen one reaches the base of the 

 myelinated layer where it branches to go to the different gyri 

 sooner than in the normal birds. 



There is no abnormal increase in cells in the cortex, especially 

 in the molecular layer. No thickening of the pia mater is recog- 

 nizable; the capillaries in the cortical layer seem not to be as 

 numerous as in the normal. 



From the above findings in the cerebellum we may easily 

 conclude that the nucleus cerebellaris medialis and lateralis 

 do not play a very important part in the affection observed in 

 the birds. The chief changes consist, however, in a diffuse 

 reduction of the molecular layer on the whole surface of the 

 cerebellum and especially in a reduction in the lateral myelinated 

 portion of the cerebellar body with its cortical layer near the 

 cerebellar peduncle. In reference to the cerebellar peduncle, 

 further description will be given later. 



