OUTLINE FOR. LABORATORY STUDY OF THE CHICK 351 



and the tissue looks perfectly clear or slightly opaque. It may be 

 quite transparent as the protein coagulate is somewhat white, but 

 aU yellow or reddish color should be bleached away. 



V. Washing. Rinse thoroughly in running tap water or through 

 several changes of water until the odor of ammonia is quite gone. 



VI. Dehydration. Pass gradually through alcohol solutions, 30 

 per cent., 50 per cent., 60 per cent., 70 per cent., 80 per cent., 95 

 per cent., and last through absolute alcohol. The time required 

 for dehydration will vary with the size of the material, but in either 

 95 per , cent, solution or in absolute alcohol the tissue should remain 

 until well hardened, twenty-four hours or more. Dehydration is 

 completed by passing from absolute alcohol, to a fluid one-half 

 absolute alcohol and one-half benzol; thence for a few days to pure 

 benzol. 



VII. Clarifying. From benzol the material is finally clarified 

 in winter-green oil or any other standard clearer, and put up in its 

 final position in the museum jar. 



In commenting on this method Dr. A. F. Contant says: "I have 

 foimd this to work very successfully in the injection of the lympha- 

 tics of the human skin, which, as you know, is a rather delicate 

 injection and has been difficult of demonstration by other methods. 

 With this method, however, I have prepared whole portions, as the 

 side of the face, the leg, etc., of small animals and embryos which 

 show clearly the whole course of the lymphatic vessels and nodes, in 

 situ, and their relations to surrounding parts." 



EQUIPMENT FOR THE DISSECTION LABORATORY 



Figure 84 illustrates some essential equipment for the dissection 

 laboratory. The equipment should consist of a pump. No. i, which 

 forces air through the rubber tube. No. 2, into the pressure tank. No. 

 4, which is guarded by the valve at No. 3. At dial. No. 5, indicates 

 the pressure of the air within the tank. The air as needed is re- 

 leased through an outlet valve. The air now passes through the 

 rubber tube, No. 6, into the left arm of the manometer at No. 7. 

 The manometer is simply a glass tubing filled with mercury to the 

 point indicated at No. 7. By the side of the opposite arm there is 

 made a scale graduated in centimeters. The tube at No. 9 being 

 attached to the Y-tube, conveys air under the same pressure into 

 the injection chamber as that supporting the column of mercury 



