The reagents necessary are alcohol of 95 per cent and 85 per cent, and formalin of 4 per cent (the formaldehyde sold by druggists is 40 per cent and should be diluted ten times with water), these for preserving material for dissection; chloroform for killing specimens; glycerin for making temporary microscopic mounts, and 20 per cent nitric acid for preparing specimens for study of the nervous system. In addition there will be needed the few other materials mentioned in the following paragraphs as necessary in the preparation of injecting-fluids, the staining of fresh tissue and preserving by special methods. A list of reference books desirable in the laboratory is appended as a separate paragraph (see p. 454). =Collecting and preparing material for use in the laboratory.=--As directions have been given in the "technical notes" scattered through the book for the collecting and preparing of all the various kinds of animals chosen as subjects of the laboratory exercises, it will only be necessary to give here directions for making certain special mixtures and for the special preparation of specimens by injection, etc. Specimens to be used for dissection should be kept in alcohol of 85 per cent or in formalin of 4 per cent. Alcohol is better for the earthworm, but for the other examples formalin is either better or as good, and as it is much cheaper it may well be chosen for the general preservative. _Methyl green_, a stain used for coloring fresh tissues. Dissolve the methyl green powder in water, using about as much powder as the water will take up. Add a few drops of acetic acid. _Injecting-masses._--Injections are best made with preparations of French gelatine, but white glue will answer most purposes. For fine injection use a combination of the following: 1 part of a solution of gelatine, 1 part to 4 parts of water; 1 part of a saturated solution of lead acetate in water, and 1 part of a saturated solution of potassium bichromate in water. A mixture of these when hot gives a beautiful yellow injection-mass which, filtered, will pass through the finest capillaries. For different colorings use dry paints, which come in ultramarine blue, vermilion, and green. The gelatine should be thoroughly soaked before the coloring-matter is added. A mistake is generally made in using the injection-mass too thick. One part by weight of gelatine to six or even more parts of water is a good proportion. The gelatine as well as glue-masses should be made in a water-bath, which consists of one dish placed within another outer one containing warm water. The mass should be injected warm, _not hot_, after which the injected specimen is to be placed in cold water until the injecting-mass has set. Glue (the ordinary white kind) can be used for most injections just as the gelatine was used, but should not be so much diluted. All injection-masses should be filtered through a cloth before using.