2 Mason — Central Nervous System of Reptiles^ etc. 



much interest, many of which can be examined remarkably 

 well in cold-blooded animals. 



Before describing tlie method of making preparations which 

 I employ, a few features of the process of Stieda will be no- 

 ticed. This observer places the entire brains of small animals, 

 iirst in a solution of 80-90 per cent, alcohol, which has been 

 tinted yellow by iodine. As soon as the piece feels firm to the 

 touch (one to four days according to the size of the specimen) 

 it is placed in a dark j^ellow solution of bichromate of potash, 

 care being taken to use a large excess of the solution. After 

 a time varying from three weeks to three months, the hard- 

 ened part is placed in strong ammoniacal carmine, and is 

 removed after from one to five days, placed in alcohol, and 

 after all excess of carmine has been removed, is ready for 

 section. 



By this process Stieda has been able to prepare sections in 

 a long unbroken series, of the brains of mice, frogs, etc., sav- 

 ing thereby the risks of several transfers. 



My own method is the old one, except in regard to the 

 solutions for hardening, A two per cent, solution of bichro- 

 mate of potash has given me excellent preparations, also the 

 solution of Clarke, which consists of a solution (1-800) of 

 chromic acid, to each ounce of which a grain of bichromate of 

 potash is added. So far I prefer to stain after cutting. At 

 least two transfers may be avoided by using a siphon tube, to 

 remove alcohol or water, and with the flattened spoons of Se- 

 guin, there is but little danger of injuring the sections. After 

 the piece has remained from three to five weeks in the two per 

 cent, bichromate solution, which it is well to renew every two 

 weeks at least, it is placed in Ivanoff 's modification of Miiller's 

 fluid, which consists of one or more parts of sulphate of soda, 

 until read}^ for section, when it is transferred to alcohol for a 

 lew minutes. 



The membranes of the cord ought not to be i-emoved 

 until just before making the sections, or until the part is 

 thoroughly hardened, otherwise deformity will surely result, 

 showins: itself in an oval instead of circular central canal. 

 "When an unbroken series is not desired, it is better to make 

 sections with the membranes on. After cutting, the sec- 



