6 'Journal of Comparative Neurology and Psychology. 



contrast coloring. I tried all kinds of contrast stains, of which 

 Mayer's paracarmin appears to me to be preferable to other cell 

 stains as it takes less time than other carmins and the stain is 

 stronger. The paracarmin coloring is preferable to that by any 

 anilin stain on account of its permanence. 



Finally some supplemenatry preparations have been made of 

 the brains of teleosts and selachians by Bielchowsky's method 

 and Ramon y Cajal's new alcohol-ammonia-silver method, 

 which are great acquisitions for the investigation of fiber tracts. 

 Bielchowsky's method was applied, among others, to a brain 

 which had been for more than a year in formalin of lo per cent, 

 and grave the most beautiful results for the unmedullated tracts, 

 while the medullated are pretty clear for orientation by reason of 

 their brown color. I made celloidin sections of it and even applied 

 it to a series of celloidin sections fixed to the slide by means of a 

 celloidin film. This goes very well provided the whole section is 

 everywhere fixed to the slide with no free edges or wrinkles, for the 

 silver precipitates in the wrinkles and between the glass and the 

 celloidin where it is not fast to the slide to such a degree some- 

 times that the neighboring sections wholly fail of impregnation. 

 This is a beautiful illustration of the behavior of silver in his- 

 tological technic — that it precipitates in small spaces, either 

 natural or artificial. Another thing to remember when applying 

 Bielchowsky's method in celloidin is to extract as little formalin 

 as possible from the embedded piece before and after embedding. 

 Accordingly, it is impossible to keep a celloidin-embedded block 

 in alcohol in the customary way. The formalin is extracted from 

 it in a few days and the preparations do not succeed well. For 

 keeping the celloidin block Apathy's method of enveloping the 

 whole block in gelatin to prevent its becoming too hard is good. 

 I preferred, however, to keep the block in 80 per cent, alcohol 

 with 10 per cent, formalin. I made no paraffin sections by this 

 method, but after my celloidin experience I fully trust Biel- 

 chowsky's statement that this is quite possible. 



In studying the following pages the reader is recommended to 

 make frequent reference to the figures — not only the sections 

 figured on Plates I to VII, but also the diagrams on Plates VIII 

 to XVI, which are designed to summarize the several chapters. 



