_Insects._--Injections of insects may be made by forcing the injection into the general abdominal cavity, when it passes into the dorsal vessel and is afterwards distributed throughout the system. The superfluous injection is then washed away, and such parts of the body as may be required removed for examination.
Natural injection of Medusæ may be effected without injuring the vessels, with an opening at the side remote from it. The medusa must be placed in a glass vessel, with the bell downwards, and a bell-jar ending in a narrow tube above is placed over it and made air-tight; the medusa is then covered with the injection-mass, the air in the glass is exhausted, and as the sea-water runs out by slits in the lower side of the annular canal, the coloured fluid runs in. In the case of leeches and large species of earthworms, the natural injection is made from the ventral sinus. In all cases a glass tube is used, with a finely drawn-out point. The injection is complete when the injection issues from the counter-opening. Besides the animals mentioned, large caterpillars, beetles, and larvæ of various kinds are favourable objects for injection; the glass cannula being introduced into the posterior end of the dorsal vessel, and the counter-opening made in the ventral vessel, and _vice versâ_.
_Staining Living Protoplasm with Bismarck Brown._--Henneguy having treated _Paramœcium aurelia_ with an aqueous solution of aniline brown (known as “Bismarck Brown”), found that they assumed an intense yellow-brown colour. The colour first appears in the vacuoles of the protoplasm, and then in the protoplasm itself, the nucleus generally remaining colourless, and becoming more visible than in the normal state. If a yellow-tinted paramœcium be compressed so as to cause a small quantity of the protoplasm to exude, it is seen that it really is the protoplasmic substance which becomes coloured. All the Infusoria may be stained with Bismarck brown, but no other aniline colour employed exhibits the same property--they merely stain the Infusoria after death, and are in fact poisonous. Living protoplasm does not as a rule absorb colouring matters, and as Infusoria are chiefly composed of protoplasm, attempts have been made to ascertain whether protoplasm in general, of animal or vegetable origin, behaved in the same way in the presence of aniline brown. A tolerably strong solution of Bismarck brown was therefore injected under the skin of the back of several frogs. After some hours the tissues became uniformly tinted a deep yellow; the muscular substance especially had a very marked yellow tint. The frogs did not appear in the least incommoded. Small fry of trout placed in a solution stained rapidly and continued to swim about. Finally, a guinea-pig, under whose skin some powder of Bismarck brown had been introduced, soon presented a yellow staining of the buccal and anal mucous membranes and of the skin. Seeds of cress sown on cotton soaked with a concentrated solution of the Bismarck brown sprouted, and the young plants were strongly stained brown; but on crushing the tissues and examining them under the microscope, it was ascertained that the protoplasm of the cells was very feebly coloured: the vessels, on the contrary, showed a deep brown stain up to their termination of the leaf. The mycelium of a mould developed in a solution of Bismarck brown was clearly stained after having been washed in water, whilst it is known that the mycelium, which frequently forms in coloured solutions, picro-carmine, hæmatoxylin, &c., remained perfectly colourless. Other aniline colours injected under the skin of frogs stained the connective tissue as deeply as did the Bismarck brown; but the striæ of muscle remained colourless. We may conclude, then, that Bismarck brown possesses the quality of colouring living protoplasm both in plants and in animals.