6 bulletin: museum of comparative zoology. 



is a deep brown. If pyroligneous acid is used subsequently to the 

 platinic-chloride mixture, all parts of the animal become so intensely 

 black as to be useless, and the tissue is rendered extremely brittle as 

 well. The material may, however, be very readily decolorized to any 

 extent by the use of peroxide of hydrogen. Very good preparations 

 may be obtained in this way, either from tissue which is too dark from 

 the action of the picric-osmic mixture alone or from that which has in 

 addition been treated with pyrohgneous acid; the method may be 

 applied to the entire animal, or to sections uj)on the slide. Decolori- 

 zation may be controlled by watching the tissue during the process. 

 I have used the pure commercial peroxide without visible injury tO' 

 the tissue, but the rapidity of decolorization depends uy^on the strength 

 of the solution employed. 



The stains I have used have been chiefly the iron-haematoxylin of 

 Heidenhain, Mallory's (:00) connective-tissue stain, and the platinic- 

 osmic-acetic mixture of vom Rath, which was -also the fixing reagent. 

 The three stains are about equally valuable; each supplements the 

 others. The haematoxylin is best for nuclear structul-es; vom Rath's. 

 fluid is excellent for nerve-tracts and medullated fibres. The con- 

 nective-tissue stain of ^Nlallory is unexcelled for general contrast 

 and for extreme delicacy in many structures, such as the nerve- 

 endings in the cells of the eye. It is very serviceable in any tissue 

 unless the nuclei are to be particularly studied. It dififerentiates 

 nerve tracts in the brain as well as, or better than, vom Rath, since 

 the color contrast is greater, but for following the course of single 

 fibjes it is in general not as satisfactory as the latter. Mallory's stain 

 has the disadvantage, possibly, that it is rather capricious; at any 

 rate preparations in which it has been used vary greatly in value and 

 unaccountably so. But when successful,- the stain gives pictures 

 which are most excellent in the matters of delicacy and sharpness. 

 In addition to this there is the great advantage of simplicity and 

 rapidity of procedure in its use. 



The methylen-blue method has, in my hands, been uniformly 

 unsuccessful in the case of the marine copepods, though it has been 

 tried many times. It is, of course, impossible to inject the stain, and 

 if the animals are immersed in a solution the result has been negative. 

 The marine forms do not respond to such treatment in the way that 

 the fresh-water forms do (Esterly :06). 



No attempt has been made to impregnate nervous structures accord- 

 ing to the method of Golgi, and I have not obtained good results from 

 the Bielschowsky method. 



