ZOOLOGICAL STATION IN NAPLES. 225 



to flow under the cover, and thus replace the staining medium, or 

 with 



Acetic acid carmine (after Schneider), used undiluted. The 

 last-mentioned staining agent causes swelling, but still gives the 

 typical features of the karyokinetic figures. 



2. Eggs first hardened in strong nitric acid (40-50 to aq. dest. 

 60-50), then washed in distilled water until the yellowish colour, 

 due to the presence of the acid, disappears. Coloured with acetic 

 acid carmine. 



III. — Methods of Dissecting. 



For the dissection of single organs, fresh animals are generally 

 placed in dilute alcohol, or a weak chromic solution. But the 

 tissues are liable to suffer from maceration in these fluids, and 

 hence, where it is important that the tissues should be well pre- 

 served, it is advisable to use picro-sulphuric acid, regardless of the 

 injurious effects of the same on the dissecting instruments. The 

 hardening capacity of the picro-sulphuric acid is extremely slight, 

 but may be strengthened by the addition of chromic acid. Pre- 

 parations thus obtained, and subsequently treated with alcohol, 

 staining fluids, etc., should be transferred to creosote for further 

 dissection, as the transparency induced by this medium will 

 greatly facilitate the work. 



IV. — Imbedding. 



For section cutting, objects are usually imbedded in paraffine, 

 but in low temperature, as in winter, it is necessary to work with a 

 softer paraffine than is required for summer. Instead of softening 

 by an admixture of lard, as is generally done, it is better to use a 

 paraffine which becomes soft in summer, on account of its contain- 

 ing liquid hydrocarbons. 



Preparatory to imbedding, the objects are removed from abso- 

 lute alcohol * to creosote, clove-oil or chloroform, and left until 

 they become thoroughly saturated. The penetration of the clari- 

 fying fluid may, in some cases, be advantageously hastened by 

 warming a Httle. They are next placed in soft paraffine, heated to 

 about 50° C. over a water bath, and allowed to remain for an 

 hour or so. The soft paraffine is then turned off and replaced by 

 * In many cases a lower grade of alcohol will sufifice. 



