ARTERIAL BLOOD PRESSURE IN A MAMMAL 235 



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 experimenter attend 

 strictly and at all times to anesthetizing the animal; recovery jrom 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. cf 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 cut toward the heart, 

 and letting it extend about half way across the artery. Introduce a cannula 

 through the opening toward the heart, and tie it firmly with the second liga- 

 ture. Connect the cannula with the rubber tubing to the vertical glass tube. 



When all is ready remove the bulldog forceps on the artery, following 

 which the blood will flow freely from the artery into the tube until the pressure 

 from the column of liquid is just equal to that inside the artery itself. If an 

 anti-coagulating fluid, 10 per cent magnesium sulphate, is first introduced 

 into the vertical tube of fortunate height little blood will be lost and probably 

 clotting at the cannula will be delayed for some minutes. The mounting t 

 of the blood into the empty tube makes indeed a more striking demonstration, 

 but it has the disadvantage of quickly forming a clot which stops the experi- 

 ment itself. 



An accurate measure of the height of the top of the column above the 

 level of the cannula at the artery represents the arterial blood pressure in 

 terms of blood, or of 10 per cent magnesium sulphate. The specific gravity 

 of magnesium sulphate is 1.030; of blood 1.056; of mercury 13.6. Record 

 the pressure you obtain in terms of blood and of mercury. Note also the 

 variations in pressure and account for the rhythm of each. There will be 

 a general variation of pressure, depending upon the degree of anesthesia. 

 If anesthesia is light and muscular movements happen, there will be an in- 

 crease in the blood pressure. If the anesthesia is heavy, then the blood pres- 

 sure falls. These points of variation should be marked, or recorded at once in 

 note-books. Make full notes of all accessory facts which would aid you to 

 explain the variation in blood pressure, such as size of the animal, rate of res- 

 piration, rate of heartbeat, the variations in anesthesia, the presence of the 

 reflexes, etc., etc. 



Chloroform the animal to kill it, and note the change in blood pressure 

 during the process 



