182 CIRCULATION OF THE BLOOD 



It has long been known that by artificially supplying blood to the extir- 

 pated heart of cold-blooded animals., activity can be maintained for a con- 

 siderable time (Ludwig). Later Newell Martin and Langendorff accom- 

 plished the same thing with the heart of warm-blooded animals. For this 

 purpose blood is led into the aorta by means of a cannula tied in it and 

 directed toward the heart. Because the semilunar valves are closed by the 

 pressure from the cannula, the blood flows through the coronary vessels to 

 the right auricle, whence it is allowed to escape. Numerous observations have 

 been made on such preparations as to the way a heart works under different 

 conditions when separated from the central nervous system and from the 

 blood vessels; and as to the effect which various agents exercise on the per- 

 formance of the heart. 



However it is not necessary to use blood as the nutrient fluid in order to 

 keep the heart beating, for several hours at least; for both in cold-blooded 

 (Ringer) and in warm-blooded animals (Locke) a solution of certain inor- 

 ganic salts has been found sufficient (0.1 per cent NaHC0 3 , 0.1 per cent CaCl 2 , 

 0.075 per cent KC1, eight per cent NaCl). For the warm-blooded heart the 

 fluid must be saturated with oxygen. By addition of a small quantity of 

 dextrose also this artificial serum is still more effective. 



The significance of these substances has been discussed already at page 25. 

 Here it may be added only that the favorable action of the NaHC0 3 might 

 be due to the C0 2 , for with a sufficient supply of oxygen, carbon dioxide 

 actually increases the energy of the isolated frog's heart (Gothlin). 



The great tenacity of life exhibited by the exsected heart is truly remark- 

 able. By artificial perfusion with the above-mentioned solution (and dex- 

 trose), Kuliabko obtained well-marked contractions of the entire heart of 

 the rabbit five days after the death of the animal. He also succeeded in 

 completely reviving the heart of a four-year-old boy who had died of pneu- 

 monia duplex and catarrhus intestinalis, twenty hours after death. 



Moreover the tenacity of life in the different portions of the heart is very 

 different. When the heart is dying, the left ventricle stops first, then the right, 

 but the auricles continue to beat for a considerably longer time. Finally the 

 pulsations of the left auricle cease and last of all those of the right. Even then 

 the contractions of the great veins always go on for a time, and only when these 

 have ceased is the heart entirely dead. 



When the oxygen supply to the heart is cut off the heart beats become less 

 and less frequent as asphyxiation comes on, and other changes make their 

 appearance which cannot be discussed here. However it should be observed 

 that the heart, especially of cold-blooded animals, has great power of resist- 

 ance against oxygen hunger (cf. page 28). 



C. THE BEHAVIOR OF HEART MUSCLE UNDER DIRECT STIMULATION 



If the heart muscle be stimulated with induction currents of different 

 strength, either it does not contract at all, or it contracts to its utmost extent 

 (Bowditch). The response of the heart muscle therefore is always maximal, 

 while the contraction of skeletal muscle is great or small according to the 



