THE PRESERVATION OF MATERIAL 371 



At the moment when the cannula is securely fastened into the 

 vessel, the clamp is to be removed from the connecting tube and 

 the fluid allowed to run in. At the beginning of the process a little 

 care in arranging the animal will be amply rewarded by con- 

 venience in dissection. The hind limb on the side opposite the 

 incision should be drawn backward. The front limbs should be 

 drawn apart, so that the breast is well exposed, and held in this 

 position by a thick cord, or, better, a stout flexible wire, passing 

 around the back of the animal. The body should be turned slightly 

 to the operator's left. 



The animal is sufflciently embalmed in two hours. About eight 

 animals may easily be kept on the table by one operator, provided 

 he has at his disposal a sufficient number of cannulae, one for each 

 specimen, since the first may be taken off the apparatus after the 

 eighth has been put on. After some practice the number can be 

 greatly increased. 



Since small difficulties frequently occur in the process, especially 

 in placing the cannulae and in keeping them clear of obstruction, 

 a number of points may be mentioned which indicate to the oper- 

 ator just how the operation is succeeding. The entrance of the 

 cannula into the artery, in the first place, is usually accompanied 

 by a slight rise of blood into its tip. General muscle contractions 

 in the recently killed animal are a safe indication of uniform flow 

 of the fluid to these and also other parts of the body, and no clogging 

 of the vessels need be feared. The fluid may usually be observed 

 running in the cannula, and, of course, falling in the reservoir. 

 Finally, there are characteristic changes in the body. The abdo- 

 men becomes greatly distended, the subcutaneous tissue swollen, 

 the eyes protrude, and there is usually more or less frothing at the 

 nose. Leakage, either in the area of the incision or at the nose, 

 is sometimes a sign of too much pressure. In the former case the 

 leakage is frequently behind the cannula, and may be stopped by 

 artery forceps. In the latter case there is no recourse but to confine 

 the fluid to the nasal cavity by tying the nostrils. 



After the embalming process the rubber tube is disconnected 

 from the cannula, the latter being left carefully in place and closed 

 by a stopper made by tying a short piece of rubber tubing in a knot. 

 The animal is then set aside, preferably for twenty-four hours to 



