THE KELATION OF THE HEART-BEAT TO ELECTROLYTES. 179 



In working at the action of salts on the heart I was led, for reasons 

 which need not be entered into here, to investigate the action of salts 

 of the rare earth metals such as lanthanum, yttrium, neo-dymium — in 

 all eleven were studied. 



These salts in aqueous solution yield trivalent ions, La • • * 

 Nd • • •, etc. Unlike the salts of other metals yielding simple 

 trivalent ions (such as aluminium, gold, iron, etc.), these salts of the 

 rare earths do not render the solution acid in reaction — they do not 

 undergo hydrolytic dissociation. I found that remarkably small con- 

 centrations of these salts in "neutral" solution sufficed to stop the 

 heart. Thus the frog's heart is invariably stopped within a few 

 minutes, generally within thirty seconds, by a solution containing 

 •00001 gram molecules per litre of either of these rare earths, and I 

 have often seen it stopped by a concentration of one-millionth mole- 

 cular. I find the same action on the heart of the rabbit and of the 

 ray as on that of the frog. 



Studied in detail on the frog's heart, the effect of tJic simple trivalent 

 ion parallels that of acid in every p)articular. The mode of arrest, the 

 absence of recovery, or the slovj and imperfect recovery on washing out vnth 

 "neutral saline'' and the immediate and complete recovery on the use of 

 alkali, are cdl reproduced exactly* 



How are these phenomena to be interpreted ? 



Can we discover any physico-chemical explanation for the close 

 similarity in their action on the heart of these ions, the hydrogen ion 

 and the ion of the trivalent rare earth, which are so difierent chemi- 

 cally, so widely different in their mobilities and their volumes ? 



Let us first review very briefly what other considerations have led 

 physiologists to infer as to the nature of that subtle mechanism by 

 which muscular tissues like that of the heart transform chemical into 

 mechanical energy with such high efficiency. 



The recent work of A. V. Hill on the time relations between heat 



* Quantitative investigation shows that these simple trivalent ions are more powerful 

 than the chemically er[uivalent concentration of hydrogen ions in their effect on the 

 heart. And thus it happens that if the activities of solutions yielding trivalent ions 

 which do undergo hydrolytic dissociation are compared with those which do not, the 

 latter are found more powerful in their action on the heart. For instance, t;iking equi- 

 niolecular solutions of aluminium, scandium, and lanthanum chlorides, the Al • " • 

 liberated in the first solution combines to some extent with the OH' in the water, form- 

 ing an almost undissociated hydro.xide and liberating an equivalent of H" (3 H* for 

 every Al • • •). Tims the solution becomes acid. In the lanthanum solution there is no 

 hydrolysis, for lanthanum hydroxide is strongly dissociated. Thus the solution remains 

 "neutral," and contains its full complement of La • • •. The case of scandium is 

 intermediate : its solution is less acid than the Al solution. Now it is found that while all 

 three solutions produce the same kind of effect on the heart, the lanthanum solution is [he 

 most and the aluminium solution the least powerful of the three. 



