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HISTOLOGICAL METHODS.

A cat, dog, rabbit, or Guinea pig will furnish parts from which sections can be cut for the study of histology.  Whichever animal is selected should be young and well developed.  Put it under influence of chloroform, and open into the cavity of the chest; make an incision into the right ventricle, and allow the animal to bleed to death; cut the trachea and inject the lungs with a solution of one and a half drachms of chromic acid in one quart of water, care being taken not to overdistend the lung.  Tie the severed end to prevent the escape of the fluid, and carefully remove the lung.  It is a difficult thing to do this without rupturing it, but with care and patience it can be done.  Place the lungs in a solution of the same strength as used for injecting; after fifteen or twenty hours change it to a fresh solution, and allow it to remain for about a month, and then change it to rectified spirits, in which it may remain until required.

Cut the tongue into several transverse and longitudinal pieces, also the small intestines, and put them into a solution of fifteen and one-half grains chromic acid, thirty grammes bichromate of potash, and three pints of water; change the solution the next day, and let them remain two weeks and then place in spirits.  Cut longitudinal and transverse portions of the stomach and large intestines, wash in a weak solution of salt and water, and put them in the same solution as used for the lungs, and treat similarly.

Cut the kidneys longitudinally and transversely, and put them in a solution of six and one-half drachms bichromate of potash, two and one-half drachms sodium sulphate, one quart of water; change the solution the next day, and at the end of four weeks transfer to alcohol.  Wash the inner surface of the bladder with salt and water, and after cutting it longitudinally and transversely, put the sections in a solution of three drachms bichromate of potash in a quart of water.  Cut the liver into small parts, and place in the same solution as used for the kidneys; change the solution after a day, and let them remain four or five weeks, then change to spirits.  The spleen and portions of the thin abdominal muscles may be placed in a solution of three drachms chromic acid to one quart of water, and transferred to alcohol after three or four weeks.  Carefully remove an eye and divide it behind the crystalline lens, put the posterior portion in a solution made by dissolving fifteen grs. chromic acid in five drachms water, and slowly adding five and one-half ounces alcohol; change to spirits in two weeks.  The lens should be put in the same solution, but should remain a few days longer.  Open the head, remove the brain, and place transverse and longitudinal sections of it in spirits for eighteen hours, then transfer to a solution of one drachm chromic acid in a quart of water, and let it remain until hard enough to cut.  Place the uterus in a solution of one and one-half drachms chromic acid in one quart of water, change to a new solution the next day, and at the end of a month transfer to alcohol.