ix CARDIAC MUSCLE AND NERVES 293 



at any rate, innocuous to the body as a whole, when introduced 

 into the circulation. 



We should, a priori, expect the best effects to result from those 

 solutions which in their chemical composition most closely 

 resemble the complex constitution of blood the natural food of 

 all the tissues. In practice, however, this is the case only to a 

 limited extent. 



A point much discussed by the various investigators has been 

 the importance of oxygen in these physiological solutions. No 

 one, however, now doubts that it represents an element indis- 

 pensable to the survival of the heart. 



Von Humboldt (1797) was the first to emphasise the vivifying 

 power of oxygen in the excised heart of the frog. Following his 

 initiative, Castell (1854) made a systematic series of researches in 

 the same direction. He found that a frog's heart placed in a moist 

 chamber at 16-20 : R. went on beating for three hours in ordinary 

 air, for twelve hours in the presence of oxygen, for about one hour 

 in presence of hydrogen or nitrogen, for a few minutes only in 

 presence of carbonic acid. 



In our own researches on the excised frog's heart (1873), con- 

 nected with a manometer, and filled with serum of pig or rabbit, 

 we observed that the frequency and force of the beats augmented 

 each time the serum already used was reinforced- by fresh 

 oxygenated serum ; the rhythm slowed down and weakened when 

 the heart was made to float in oil. The vivifying action of 

 oxygen on the frog's heart was confirmed by Rossbach and Klug. 



Langendorff (1884) experimented with the asphyxiated heart, 

 and noted that it absorbed oxygen with great rapidity, so that the 

 blood introduced into it suddenly assumed a venous hue. 



Yeo (1885) made the reduction of oxyhaemoglobin by the 

 frog's heart the subject of a methodical research. He found that 

 this reduction increased with the work done by the heart. Heffter 

 and Albanese confirmed the fact that the presence of oxygen is 

 indispensable to the maintenance of cardiac activity. 



The most exact and minute researches on asphyxia and the 

 revivification of the excised frog's heart are, however, due to 

 Oehrwall (1893-97). He studied the mode of onset and the 

 duration of asphyxia in the frog's heart filled with blood or serum, 

 through which a solution of sodium chloride or of some indifferent 

 gas was circulated, as \vell as revival by the substitution of 

 oxygenated for asphyxiated blood, or by the direct action of air 

 and oxygen. 



The importance of oxygen to the function of the heart in warm- 

 blooded animals was shown by Fano (1889-90) on the embryonic 

 chick's heart, isolated on the second or third day of incubation. 



A. Porter (1898) succeeded in keeping the isolated mammalian 

 heart alive for many hours in the presence of blood serum and 



