OUTLINE FOR LABORATORY STUDY OF THE CHICK 345 



bone saw and the scalpel. The organs may now be studied from 

 each side. To make a longitudinal section through the median line, 

 select a small bird, one weighing not more than 2 poimds, kill, 

 and preserve in a 10 per cent, solution of formaldehyde for three 

 days. Then with a sharp, thin, long-bladed knife make an incision 

 at one sweep through the median line of the body down to the back 

 bone, and with the bone saw section through the vertebrae. If it is 

 difiB.cult to cut through the breast-bone, saw through before making 

 the incision. In small birds the entire cut may be made without 

 the aid of the saw. 



Directions for the Study of Arteries. — ^Arteries should be injected. 

 Veins are usually more or less filled with blood so that the tracing of 

 these is not so difficult as the tracing of uninjected arteries. Nerves 

 are white and no difficulty is usually encountered in tracing them. 



The courses of arteries, veins, and nerves are side by side, and 

 many of them, as in mammals, are arranged in the order of veins, 

 arteries, nerves, the veins being in fron t. 



The injection apparatus consists of the following parts: air-com- 

 pression chamber, to which is attached a pressure pump. A mano- 

 meter made of glass tubing 6 milhneters in diameter, inside measure- 

 ment. This tube is partly filled with mercury, and a scale in centi- 

 meters is made from the top of the right-hand tube (Fig. 84, No. 8). 

 This ruling, or gauge, should be about 15 centimeters long. Extend- 

 ing from the right extremity of the U-tube is a small rubber tubing 

 which is attached to the chamber containing the injection fluid; 

 and extending from the inferior part of this chamber is another tub- 

 ing which has the injection needle attached to the free end. 



The injection should be done under 120 millimeters pressure. 

 The stop cock of the pressure chamber is released sufficiently to 

 raise the mercury in the U-tube six centuneters, which multiplied 

 by 2, the amount of work required to raise two columns, makes 120 

 millimeters pressure. If this pressure be maintained, all vessels 

 should be injected without rupture. The same process may be used 

 in injecting the air cells through the trachea. 



The injecting material may consist of one part finely sifted plaster 

 of Paris, four parts water, and sufficient gentian violet to make a 

 violet color. For the coloring, red aniline may be used in preparing 

 this material. The dye should be dissolved in the water to be used 

 Lq making the injection Uquid. Caution must be used and the 

 work rapidly done, as the plaster soon sets, or becomes soUd, in the 



