( 20 ) 



can l)e seen in fig. IJ (tiie same preparation more ijiglily magnified) 

 tlie cells to the right of the arrow exhibit abnormalities clearly 

 shown by fig. 12. Normal Amnion's pyramid-cells both of cat and 

 rabbit (in the case of the former they are of larger size) colour well 

 witli toluidine blue; the type is polygonal, with slightly rounded 

 corners. The nucleus is large, and tinted very slightly or not at all 

 with blue; the nucleolus is darkblue ^). 



If these be compared with the cells of the right half of the 

 Amnion's horn of tig. JO, as they are represented highly magnified 

 in fig. 12, hardly a single cell will be seen with a nucleus visible; 

 the protoplasm of the cells is homogeneous and dark in colour. 

 Almost all the cells have heavy coarse neurones; a few have the 

 characteristic appearance of injured ganglion cells. It is remarkable 

 that affected and unaffected cells do not occur together in the same 

 sagittal region, or only in a slight degree; the two regions may practically 

 be divided by a line. The boundaries are so clear as to be immediately 

 noticeable, even in van Giksox preparations. I shall not quote as an 

 example of this the left Ammon's horn of cat N". 3, as the objection 

 might be put forward that the hemisphere of this side had been prima- 

 rily injured. But in the case of a rabbit, where the most caudal 

 |)art of the callosum together wilh the underlying fibres'), the 

 |)salterium, had been touched, the same thing is very apparent in 

 VAX GiEsoN preparations. The exact division between affected and 

 unaffected cells I hope to give later. 



The other elements of the cornu Ammonis — the fascia dentata 

 cells — were found to be unaltered, as were also the ammon-jiyramids 

 in a more ventral ])Osition in cat 3. I'he rabbit above-mentioned 

 showed, in connection with the abnormal relative position of the 

 Ammon's formation in rodentia as compared to carnivora — the 

 distribution of the cells somewhat otherwise; in princii)le this makes 

 no difference. 



In judging the results of experiments like the above, one ought, 

 in my opinion, to take up the position already given by vox Guddkx. 

 A cell, which degenerates after cutting of an axis-cylinder, gives 

 origin to that axis-cylinder. The wider interpretation given to the 

 degenerating cells, viz. that they might also be the elements to which 

 the cut axis-cylinder leads, is in certain circumstances certainly correct, 

 but only in the case of newborn operated animals, perhaps also in 

 the case of some long-existing lesions, or in a few exceptional cases 



1) I disregard here the histological differences of the pyramidal cells distinguished 

 by GoLc.i, Cajal, Köi.liker etc., which belong to the Ammon's horn. 

 ~) Fornix normal on both sides. 



