THE PREPARATION OF MATERIAL. 285 



the ligature, which may then be easily passed around the vessel in 

 proper position for tying. 



X. How to inject the Catfish. Anaesthetize the fish by placing it 

 in a small quantity of water to which a little chloroform or ether has 

 been added. As soon as it is quiet, cut off the dorsal spine. Place the 

 fish on its back, and open the body cavity by a median ventral slit. 

 Continue the cut forward through the bones of the pectoral arch, 

 taking care not to injure the internal organs. Separate the cut edges 

 by pressing down on both pectoral spines at once, thus disclosing the 

 heart lying in its pericardial sac. 



In a specimen intended for complete dissection, it will be conven- 

 ient to inject only that part of the circulatory system which carries 

 venous blood. Before the blood vessels can be filled with the injection 

 mass, they must be emptied of their contents. To get the blood out, 

 make a slit with fine scissors in the ventricle, another in the venous 

 sinus, another in each of the veins entering the liver from behind, and 

 another in the vein entering each kidney from behind. Sop up all the 

 blood that can be induced to flow from these incisions, with a soft 

 sponge moistened with water, or, better, with normal salt solution, 

 Then inject. Fill the syringe with the injection mass well shaken. 

 Insert its cannula into the arterial bulb through the slit in the ven- 

 tricle, ligature the nozzle of the cannula, and inject forward to fill the 

 branchial aorta and its branches. Withdraw the cannula, and tighten 

 the ligature to prevent the escape of the injection. Insert the cannula 

 in turn in each of the other incisions, ligature, and inject backward. 

 A very small cannula may be needed for injecting the veins which 

 return the blood to the kidneys. If the operation be properly per- 

 formed, the arteries (except the branchial) may be recognized in dis- 

 secting by their not being injected. 



XI. How to inject the Frog or the Turtle. Anaesthetize the frog 

 with chloroform or ether. Open the abdominal cavity by a median 

 ventral incision. Continue the cut forward through the shoulder girdle 

 a little to one side of the median line. Fasten the edges of the cut 

 apart, and disclose the heart. With sharp scissors snip off the. point 

 of the ventricle, and remove the blood with a moist sponge. 



The arterial system of the frog is very easily injected. Insert the 

 cannula through the ventricle into the base of the arterial trunk, liga- 

 ture, and inject forward. Nothing more will be necessary for filling 

 the arterial half of the circulatory system, and this will answer our 

 present purpose. 



After opening the body of the turtle as directed in the text (p. 200), 

 the method of procedure is practically the same as for the frog. 



