412 



VETEEINARY PHYSIOLOGY 



These methods, of course, give no measurement of the 

 normal output of the heart. 



B. Indirect Methods. 

 1. The Oxygen Method. — (1) By finding the amount of 

 oxygen which the blood gains per unit of time iu passing 

 through the lungs, and (2) the amount of oxygen which is 

 taken from the lungs per unit of time, the amount of blood 

 passing through the lungs, i.e. leaving the right ventricle 

 may be calculated. Since the right and left ventricles must 

 discharge equal amounts of blood, the output of the left 

 ventricle is thus ascertained. 



100 100 100 100 100 100 Cc. Blood. 



Fig. 177. — To illustrate the method of determining the amount of blood 

 leaving the right ventricle. The inverted funnel represents the lungs 

 from which 30 e.c. of O3 have been taken up by tlie blood. The 

 blood has gained 5 c.c. of Oo per 100 c.e. Therefore 600 cc. of 

 blood must have passed through the lungs, i.e. left the right ventricle. 



(1) The amount of oxygen in the blood is determined as 

 described on p. 497 (Practical Physiology). To ascertain 

 the amount of oxygen in the blood going to the lungs, 

 blood from a vein is taken ; for the amount of oxygen in 

 the blood leaving the heart the blood from an artery is taken. 



If lower animals, e.g. goats, are used, the method may be 

 made even more accurate by taking blood by means of 

 trocars simultaneously from the right (venous blood) 

 and left ventricle (arterial blood). 



(2) The amount of oxygen taken from the lungs is 

 determined by means of the Douglas bag (p. 261). Suppose 

 the blood gains 5 per cent, of oxygen, and suppose that in 



