562 CIRCULATION OP BLOOD AND LYMPH. 



The dividing line between the ancient and the modern views of the heart 

 beat is found in the work of William Harvey (1628). Before his time physi- 

 cians thouglit along the lines laid down by the ancient masters, Hippocrates, 

 Aristotle, and Galen, in that they believed that the diastole of the lieart is 

 the active part of the beat. They beheved that the heart dilated at the mo- 

 ment of the apex beat, the dilatation being due to the implanted heat, the 

 vital spirits, a special pulsatile force, etc. The arteries dilated at the same 

 time for a similar reason. For a period of over two thousand years men's 

 minds were so chained to this belief that they apparently could take no other 

 view. Harvey, however, had the boldness and originality to look at the 

 matter differently. He saw and proved that the active movement of the heart 

 is a contraction during systole, which drives blood out of the ventricles into the 

 arteries, and consequently that the pulse of the arteries is not due to their 

 active dilatation, but to a distension by the blood forced into them. Harvey 

 may be considered also as the founder of the myogenic theory of the heart 

 beat. For although he did not speculate concerning the cause of the beat, 

 he taught that the systole is an active contraction of the heart's own muscu- 

 lature not dependent upon any external influence. In the same century the 

 first neurogenic hypothesis was formulated. Willis conceived that the cere- 

 bellum controls the activity of the involuntary organs, including the heart. 

 The animal spirits engendered in the cerebellum were conveyed to the heart 

 by the vagus nerve and caused its beat. Borelli formulated a somewhat 

 different view. According to him the nerve juice, succus spirituosus, elabo- 

 rated in the central nervous system was transmitted to the heart through the 

 cardiac nerves and, distilling slowly into the musculature, set up an ebullition 

 wliich caused an active expansion of the fibers. This expansion constituted 

 the systole and drove the blood out of the heart. Both of these views were 

 disproved or rendered improbable largely by the work of Haller, who in 1757 

 published the second myogenic theory in a form which, somewhat modified, 

 prevails to-day. Haller believed that the contraction of the heart is due to the 

 mherent irritability of its musculature, and that the venous blood as it enters 

 the heart stimulates it to contraction. Haller's views were generally accepted 

 for some years, but some physiologists continued to believe that the heart beat 

 is controlled directly by the central nervous system. This theory found its 

 most definite expression in the work of Legallois, 1812, who advanced what 

 may be called the second neurogenic hypothesis. From experiments made 

 upon animals he concluded that the principle or force that causes the heart 

 beat is formed in the spinal cord, in all of its parts, and reaches the heart 

 through the branches of the sympathetic nerve supplying this organ. Legallois's 

 conclusions were soon shown to be erroneous, but the general view advocated 

 by him was entertained by some as late as the middle of the 19th centurj^, 

 in fact until experimental physiology had demonstrated the true functions 

 of the vagus and accelerator nerves with reference to the heart. Toward the 

 middle of the 19th century a third form of neurogenic hypothesis urose, which 

 in the beginning seems to have been due to the work or the system of Bichat. 

 According to this author the ganglionic or sympathetic system supplies the 

 tissues of the organic life, meaning thereby the visceral organs which are not 

 under the direct influence of the will. In 1844 Remak discovered that the 

 heart possesses intrinsic nerve ganglia, and this fact seems to have induced most 

 physiologists to believe that these ganglia constitute a motor center for the 

 heart, initiating and co-ordinating its beat. For a period of forty years this 

 form of the neurogenic hypothesis enjoyed almost universal acceptance. In 

 1881-83 Gaskell published experiments upon the heart of the frog and tortoise 

 in which he gave strong reasons for believing that the beat is myogenic in 

 origin, and that the intrinsic ganglia are simply a part of the inhibitory ap- 

 paratus of the heart. Since t'iat time many physiologists have adopted the 

 myogenic view. The most significant addition to our knowledge of the cause 

 of the heart beat made during the last quarter of a century is the discovery 

 that the inorganic salts of the blood and lymph play a special and essential 

 role. The facts bearing upon this interesting discovery are sufficiently 

 described in the text. 



