8 4 



CIRCULATION OF THE BLOOD 



resistance that is presented in the systemic circulation ; and the 

 anatomy of the pulmonary vessels and of the right side of the heart 

 shows that the blood must circulate in the lungs with comparative 

 facility. The right ventricle has about one-third the force of the 

 left, and the pulmonary artery will sustain a much less pressure than 

 the aorta. 



The pressure of blood in the pulmonary artery, measured by con- 

 necting a cardiometer with a trocar introduced into the pulmonary 

 artery of a living horse through one of the intercostal spaces, was 

 found to be about one-third as great as the pressure in the aorta, which 

 nearly corresponds with an estimate of the comparative power of the 

 two ventricles, judging from the thickness of their muscular walls 

 (Chauveau and Faivre). 



On microscopical examination of the circulation in the lower animals, 

 as in the frog, the movement of blood in the capillaries of the lungs 

 does not present any differences from the capillary circulation in other 

 parts, except that the vessels seem more crowded with corpuscles and 

 there is no " still layer " next their walls. 



Circulation in the Walls of the Heart. The circulation in the walls 

 of the heart does not present important peculiarities. It has been 



shown that the pressure 

 of blood in the coronary 

 arteries in the dog, dur- 

 ing the ventricular sys- 

 tole, is sufficient to supply 

 the arterioles in the sub- 

 stance of the heart with 

 blood, precisely as it is 

 supplied to the general 

 arterial system.' In a 

 number of experiments 

 in which simultaneous 

 traces of the pulse-beats 

 were obtained, it was 

 found that the coronary 

 and carotid pulses were 

 practically synchronous 

 (Martin). 



Passage of ' Blood-Cor- 



_b 



Fig. 27. Migration of leucocytes and diapedesis of red cor- 

 puscles (Councilman). 



This figure represents a portion of the mesentery of a frog 

 two hours after exposure, a, a, small arteries ; b, b, small veins ; 

 c, a few leucocytes in connective tissue ; d, d, diapedesis of red 

 corpuscles; e, e, emigration of leucocytes. 



puscles through the Walls of the Vessels {Migration and Diapedesis^}. 

 In the frog it has been observed that leucocytes sometimes pass through 

 the walls of the bloodvessels, either by means of small orifices (stro- 



