578 Stewart Paton 



or beiizol may be used before embedding in i)araftine. Cedar oil 

 Ì8 useful ìf it is desired to study the distributìon of the nerv^es prior 

 to embeddiug and cutting sections, as even large embryos become 

 semi-transparent in this medium. 



Selachian embryos of 5 — 7 mm. in lengtb may be dehydrated 

 and embedded in 3 or 4 hours after they are first placed in alcohol. 

 The weaker sulutions of alcohol seem to be far more liable to de- 

 colorize the s])ecimens than are the stronger ones. 



7) The sections are fixed upon the slide by means of albumen- 

 glycerine. After they are carefully dried it is well to paint them 

 over with '/2^ solution of celloidin. 



Following the removal of the paraffiu by xylol and the sub- 

 sequent passage through alcohols the sections are rinsed in distilled 

 water, stained for 1 — 2 hours in a Vio^ gold bath neutralized by 

 lithium carbonate, fixed by the action of a b% solution of sodium 

 hyposulphite, washed for several hours in running water, dehy- 

 drated in alcohfil, counter-stained in a 1^ solution of eosin in 

 alsolute alcohol, and mounted in the usuai way. 



Although this procedure is complicated, the results obtained are 

 far more satisfactory and uniform than those given by any other 

 method known to me. With the exercise of care the shrinkage 

 and heavy deposits of Silver so common in sections treated by the 

 technique recommended by Ramon y Cajal are avoided. 



If the sections are carefully washed after removal from the 

 fixing bath they do not fade and may be kept iudetìnitely. The 

 neurofibrils should be stained a very deep purple, almost black. 



In conclusion I desire to express my thanks to the Smithsonian 

 Institute for the prolonged opportunity given to me, of accepting the 

 exceptionable facilities for carrying on investigations, the assistance, 

 and great courtesy extended to the occupant of this Table l)y the 

 management of the Zoological Station at Naples. 



