ix CARDIAC MUSCLE AND NERVES 297 



was of the numerous organic substances present. He tested 

 glucose, serin, and paraglobulin with negative results. 



Baglioni (1905-6) was more fortunate in his experiments on the 

 isolated heart of Selachians. He knew from the previous researches 

 of Stadeler and Frerichs, and of v. Schroder, that the blood of 

 these animals is very rich in urea dissolved in the plasma. 

 According to v. Schroder the blood of the Scyllium contains on an 

 average 2'61 per cent urea. This facts explains the high values 

 of the molecular concentration of the blood in these fishes, which 

 corresponds to a solution of about 3 '5 per cent of NaCl. Straub 

 had already found that a saline solution of this concentration was 

 incapable of keeping the excised heart of these animals alive, even 

 for a short time an observation contrary to what had been 

 observed on the hearts of frogs and other poikilotherniic animals. 

 Baglioni discovered that it is possible to keep the isolated Selachian 

 heart alive for a prolonged period by treating it with a solution 

 containing a definite amount of urea. He found the most effective 

 solution to be one that contained 2 grins, of urea, and 2 grms. of 

 sodium chloride in 100 c.c. of tap water, which invariably yields 

 traces of lime salts. He further tried to determine the specific 

 action of urea, and concluded from his experimental results that it 

 promotes the contraction of the muscle cells, while larger doses 

 arrest the heart in systole. Sodium chloride, on the contrary,- 

 promotes expansion of the muscle cells, and large doses cause ' 

 diastolic arrest. 



Lambert (1905) confirmed the favourable action of urea on the 

 frog's heart ; Baglioni and Federico (1906) on that of the toad. 

 In these animals, also, urea increases the intensity and duration of - 

 the systolic phase. 



Analogous observations were made on the isolated heart of- 

 warm-blooded animals Gross (1903) carried out a methodical 

 series of experiments on the action of the various components of 

 Ringer's solution, confirming the results already obtained for the 

 frog's heart. The antagonism in the action of potassium and 

 calcium ions was marked. The former exerted a systolic, the 

 latter a diastolic action ; in large doses the first arrested the 

 heart in systole, the second in diastole. 



Langendorff and his pupils, confirming the necessity of the 

 presence of lime salts, studied the action of dissolved haemoglobin, 

 when they found that only certain mammalian hearts behave like 

 that of the frog. The hearts of cat and dog do not to any marked 

 extent exhibit toxic effects with dissolved haemoglobin, while that 

 of the rabbit behaves like the frog's heart. In explanation of this - 

 difference, Langendorff points out that the rabbit's erythrocytes - 

 contain a much larger quantity of potassium salts than those of the 

 dog or cat. Supposing that a large amount of potassic salts are 

 diffused in the rabbit's serum along with the haemoglobin, these 



