3-1 



The Naturalist. 



and owe their origin to the carmine solution in which they were 

 stained, for with careful preservation and staining they do not appear. 

 Grenadier does not think much of Beale's carmine, and draws atten- 

 tion to the great variety in the composition of commercial carmines. 

 Picro-carmine, however, perhaps on account of its containing picric 

 acid, is much more certain in its results, and in some cases it will give 

 better specimens than can be obtained by any other medium. It is a 

 pity that in commerce one can not always get it of the same quality, 

 and it often contains too much picric acid. It is therefore better to 

 make a solution for one's self. For this purpose take an ordinary 

 strong solution of carmine (about two grammes to 25 cubic centi- 

 metres of water), the ammonia of which has been allowed to evaporate 

 by long exposure to the atmosphere, and add strong picric acid in 

 water until no precipitate is formed. This will take about four parts 

 of picric acid to one of carmine. This mixture is then ready for 

 staining purposes. Of course with ArtJiropoda^ in which the chitine 

 is not very thin, the picric acid only penetrates, and not the carmine. 



Eecently Dr. Lang has recommended a mixture of equal parts of 

 1 % picro-carmine and 2 % eosin in water, specially for the planarians. 

 The object, previously hardened in alcohol, should remain in the 

 staining fluid from J to 4 days, and should afterwards be washed in 

 70 %, 90 %, and 100 % alcohol, a.intil the picric acid and superfluous 

 eosin are removed. In this way it is not only the nuclei of the 

 ganglion which are stained, but also the continuations of them, and 

 the nerve fibres become distinct if only lightly stained. 



Aniline Colours. — The use of aniline dyes in the Naples Aquarium 

 has been entirely given up — not because they are not sufficiently 

 durable (Dr. Mayer possesses a preserved section of decalcified bone, 

 stained with fuchsin and preserved in balsam, which has lost none of 

 its intensity in seven years), but because they give diffused colours. 

 Dr. Mayer is of opinion that this holds good also for the much- 

 praised eosin. In general, what one mostly wants is to get the 

 nucleus properly stained, and this can be done better and more 

 certainly by the alcoholic solutions already mentioned than by the 

 aniline derivatives which have lately come into use. Their colouring 

 matter has so little affinity for animal tissues, that deeply-stained 

 objects may have the colouring matter entirely dissolved out by 

 soaking in alcohol. Bismark-brown is in this respect an exception, 

 and although it does not dye deeply, the preparations are durable. * 

 As long, therefore, as one does not Avish to make evident the 

 difference between membranes, or the various grades of ossification, 

 &c,, it is as well to avoid this group altogether. 



