618 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [12] 



ing a large amount of yolk material, like those of Palinurus, it gives 

 better results than nitric, picric, or picro-sulphuric acid. It is not so 

 readily removed from objects as picro sulphuric acid, and for this reason 

 the latter acid would be used wherever it gives equally good prepara- 

 tions." 



This fluid is also said to be useful where the objects, such as arth- 

 ropods, are inclosed in a chitinous skin. 



For the preservation of infusoria, Blanc recommends a very dilute 

 picro-sulphuric solution, which I give here as abstracted from the Zoo- 

 logischer Anzeiger, No. 129, by Whitman. The formula is as follows : 



Picric acid, saturated solution in distilled water 100 volumes. 



Sulphuric acid (concentrated) 2 " 



Distilled water 600 " 



"To this solution, which may be employed as it is for the larvse of 

 echinoderms, medusae, and sponges, a little acetic acid (1 per cent.) is 

 added for rhizopods and infusoria — two or three drops for 15 grams of 

 the solution. The acetic acid is added in order to sharpen the outlines 

 of the nuclei and nucleoli. 



"This liquid is preferable to osmic acid, because it does not render 

 the objects non-receptive to staining fluids. 



"The entire process of hardening, washing, staining, and mounting can 

 be more expeditiously performed under the cover glass than otherwise. 

 The acid is allowed to work until the objects have become thoroughly 

 yellow. The acid is then replaced by 80 per cent, alcohol, frequently 

 renewed until the yellow color entirely disappears ; 96 per cent, alcohol 

 is next used, and then absolute alcohol. 



"The hardened objects may be stained with picro-carmine, or, better, 

 with an alcoholic solution of safranin. Five grams of safranin are dis- 

 solved in fifteen grams of absolute alcohol, the solution left standing a 

 few days, then filtered and diluted with half its volume of distilled 

 water. 



"This solution of safranin ispreferable to picro-carmine, because it colors 

 more quickly, and because one can so regulate its action as to give a 

 sharp definition to the protoplasm or the nucleus. 



"After the object has been more or less deeplj^ stained, according to 

 the end in view, it is washed in 80 per cent, alcohol, which is renewed 

 until a moment arrives when no visible clouds of color appear; at this 

 moment the 80 per cent, alcohol is replaced with absolute alcohol, and 

 this by clove oil. 



"As safranin is soluble in alcohol, the process of washing will of course 

 remove or weaken the color, but decoloration is gradual, so that one 

 needs only to watch and ai)ply the clove oil when the color has been 

 reduced to the desired intensity. * * * 



"The process of decoloration is not entirely arrested by the application 

 of clove oil, contrary to Blanc's assertion, hence it should be replaced 



