CHAP, iv.] THE VASCULAR MECHANISM. 321 



are or may be at work. The beat of the heart may for instance 

 be modified by influences bearing directly on the nutrition of the 

 heart. The tissues of the heart, like all other tissues, need an 

 adequate supply of blood of a proper quality ; if the blood vary 

 in quality or quantity the beat of the heart is correspondingly 

 affected. The excised frog's heart, as we have ;seen, continues to 

 beat for some considerable time, though apparently empty of blood. 

 After a while however the beats diminish and eventually disappear; 

 and their disappearance is greatly hastened by washing out the heart 

 with normal saline solution, which when allowed to flow through the 

 cavities of the heart readily permeates the tissues on account of 

 the peculiar construction ( 151) of the ventricular walls. If such 

 a ' washed out ' quiescent heart be fed with a perfusion cannula, in 

 the manner described ( 155), with diluted blood (of the rabbit, 

 sheep, &c.), it may be restored to functional activity. A similar 

 but less complete restoration may be witnessed if serum be used 

 instead of blood ; and a heart fed regularly with fresh supplies of 

 blood or even of serum may be kept beating for a very great 

 length of time. 



Now, serum is as we have seen a very complex fluid containing 

 several proteids, many ' extractives ' and various inorganic salts. 

 Of the proteids experiments have shewn that peptone and 

 albumose so far from being beneficial are directly poisonous to the 

 heart, that paraglobulin is without effect, but that serum-albumin 

 will maintain the beats for a long time and will restore the beats 

 of a ' washed-out ' heart. We might infer from this that serum- 

 albumin is directly concerned in the nutrition of the cardiac tissue; 

 but we are met with the striking fact that a frog's heart may be 

 maintained in vigorous pulsation for many hours, and that a 

 ' washed-out' frog's heart may be restored to vigorous pulsation by 

 being fed with normal saline fluid to which a calcium salt with a 

 trace of a potassium salt has been added 1 . On the other hand, 

 serum from which the calcium salts have been removed by 

 precipitation with sodium oxalate is powerless to maintain or to 

 restore cardiac pulsations. Obviously in the changes, whatever 

 they may be, through which such fluids as serum, milk and the like 

 (for milk and other fluids have been found efficient in this respect) 

 maintain the beat of the heart, calcium salts play an important 

 part ; and it is tempting to connect this with the relation of calcium 

 salts to the clotting of blood ( 20). We are not however justified 

 in inferring because serum is ineffective in the absence of calcium 

 salts, that the serum albumin is useless ; and, indeed the beneficial 

 effects of the calcic saline fluid are not so complete as those of serum 

 or of blood ; moreover the possible influences of the various extrac- 



1 By Kinger's Heart-Fluid, for instance, which is made by saturating in the cold 

 normal saline solution (-65 p.c. sodium chloride) with calcium phosphate, and 

 adding to 100 c.c. of the mixture, 2 c.c. of a 1 p.c. solution of potassium chloride. 



F. 21 



