258 THE CIRCULATION OF THE BLOOD 



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 ligature. 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 

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

 stration, but it has the disadvantage of quickly forming a clot which stops 

 the experiment 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 i .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 and 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 

 respiration, rate of heart-beat, 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. 



13. The Circulation Time. The circulation time is most satisfactorily 

 determined in the laboratory by introducing a saline solution of methylene 

 blue into the jugular vein on one side. Note directly the time with a stop- 

 watch until the color appears in the jugular artery and the jugular vein of 

 the opposite side. 



Anesthetize a cat or dog with a chloroform-ether mixture, tie it on the 

 animal-holder and, when the eye reflexes are lost, expose the jugular vein on 

 the right side, the carotid artery and the jugular vein on the left. Fill a 

 2-cm. hypodermic syringe with i per cent, methylene blue in physiological 

 saline, insert the needle into the right jugular vein, pointing it toward the 

 heart. Lift the left carotid artery and place under it a strip of moist white 

 paper 2 cm. wide; prepare the left jugular vein in the same way. Place the 

 animal so that these vessels are lighted to the best advantage. At a given 

 moment inject the contents of the hypodermic syringe, noting the time with a 



