148 Mr. P. A. Buxton on the 



picro-clilnr-acetic mixture ; it should not be used upon 

 osniic acid preparations. 



I have tried several stains which have proved more or 

 less useless, and I mention them below in order to save 

 others from wasting time upon them. 



Methylene Blue and Methyl Violet. — It appears 

 that the cells have little affinity for these stains. This is 

 remarkable when it is remembered to how large an extent 

 methylene blue has been used as a vital stain for the 

 nervous systems of the Arthropoda. 



Van Gieson's Stain. — This stain is useless because it 

 colours all the soft parts of the section a uniform pink 

 colour, without any of the differentiation which it gives 

 with sections of the tissues of Vertebrates. 



Various preparations of carmine were tried, because of 

 its historic interest as the only stain used by the workers 

 of thirty or forty years ago. It appears to have singularly 

 little affinity for any part of the brain of Microptenjx. 



The stains on ivhich I place most reliance are DelafieliVs 

 hcenutloxylin ivith orange G as counter-stain for preliminary 

 study, picro-nigrosin and the reduced silver and gold method 

 for the study of the course of nerve fibres, and Mann's stain for 

 the nerve cells. 



IV. Note. — Some of the fixatives and stains to which I 

 have had reason to refer are not very well known, and it 

 will perhaps be helpful if I give their compositions. The 

 picro-chlor-acetic mixture is 1 % picric acid in absolute 

 alcohol, G parts; chloroform 1 part; formalin (40%) 

 1 part ; glacial acetic acid | part. Fix twenty-four hours, 

 then three days in 90 % alcohol. Barrel's fluid consists of 

 osmic acid (Os 04) 1 gm. ; acetic acid 10 c.c. ; platinum 

 chloride 1 gm. ; chromic acid 1*5 gm.; and distilled water 

 175 c.c. 



The spirit soap which is recommended as a reagent 

 for softening chitin is one of the official preparations of 

 the German Pharmacopoeia : 6 gms. of olive oil are 

 saponified with 7 gms. of a solution of potassium hydroxide ; 

 to this is added alcohol 30 gms., water 17 c.c. (Kurt Bedau. 

 Zeitschr. f. wiss. Zoologie, Vol. 97, p. 418, 1910-11). 



Of the stains the following should perhaj)s be described. 

 The picro-nigrosin I used was made up as follows : 1 vol. 

 1 % aqueous solution of nigrosin ; 9 vols, saturated aqueous 

 solution of picric acid. The fact that the various authors 



