ARTERIAL BLOOD PRESSURE IN A MAMMAL 257 



tained. A tabulation of these results will usually enable one to judge the 

 influence of each of the various factors recommended in the experiment. 



11. Influence of the Cardiac Nerves on the Terrapin's Heart. 

 Instead of the frog one may use the terrapin in the above experiment. 

 In this animal the sympathetic can very readily be isolated, and accelerator 

 fibers have been described for it. In the experiments of the laboratory of 

 the author it has been very difficult to demonstrate very marked cases of 

 cardiac acceleration. The vagus produces inhibitions which differ from 

 the effects in the frog in that complete inhibitions of the ventricle are followed 

 by contractions that are apparently at once maximal, see figure 179. In 

 the frog the ventricular contractions when they reappear are at first slight, 

 but gradually increase in amplitude until they have their former value. 



12. The Arterial Blood Pressure in a Mammal. The arterial blood 

 pressure may be measured on the anesthetized cat, dog, or rabbit. Simple 

 blood pressure was originally measured by Hale's method of connecting 

 the artery with a vertical tube and allowing the blood to flow freely into 

 the tube until a column was raised to the height which balanced the pressure 

 in the vessel. This simple method is decidedly the best for the beginner, 

 since it does not nee ssitate the use of very complicated apparatus. At the 

 same time it gives practice in anesthesia and in operations under anesthetics, 

 and therefore serves as a good preparation for the more complicated ex- 

 periments which follow. 



The necessary apparatus should be prepared first, as follows: A vertical 

 tube supported on a stand with a scale graduated in the metric system, as- 

 sorted cannulae of approximately the size of the carotid artery of the animal 

 to be operated on, linen- thread ligatures, dissecting set in good condition, 

 an animal-holder with strings or straps firmly to fasten the anesthetized 

 animal, a chloroform-ether mixture for dogs (or other anesthetic according 

 to the animal to be used). Four men should be assigned to perform this 

 experiment. While two are anesthetizing and preparing the animal, two 

 should arrange the apparatus as nearly ready for connecting with the 

 artery as possible. When all the apparatus is arranged and the animal 

 anesthetized, it should be tied firmly to the animal-holder. Let one experi- 

 menter attend strictly and at all times to anesthetizing the animal; recovery 

 from the anesthesia must not occur. Let the operator quickly expose about 

 3 cm. of the carotid artery by making an incision through the skin of the 

 neck 5 cm. long, and dissecting down between the muscles. Separate the 

 carotid from the adherent vagus nerve by tearing the connective tissue with 

 the scalpel handle, freeing the vessel from about 2 to 3 cm. of its length. 

 Lay two loose ligatures of linen thread around the vessel, place a small 

 bulldog forceps on the exposed artery nearest the heart, and ligate the end 

 nearest the head with one of the ligatures. Take up the intervening artery 

 with strong forceps and make a V-shaped cut near the ligature, pointing the 

 17 



