ix CARDIAC MUSCLE AND NERVES 295 



Arguments in favour of this last hypothesis are not wanting, 

 but the first must also be admitted as credible, until it is directly 

 contradicted by experiment. 



C. Ludwig (1868) was the first who employed the method of 

 artificial circulation in excised organs, in studying their survival. 

 The primitive physiological solution, consisting of a dilute solution 

 of sodium chloride (0*50-0'75 per cent), was largely used by him 

 and his school as a substitute for defibrinated blood, in experi- 

 menting on the metabolism of excised organs. A little serum 

 added to the saline will keep up the vitality of the excised heart 

 of a frog for a very long time. 



Kronecker and Stirling (1875), however, found that the beats 

 of a frog's heart tied by the ventricle to a cannula (Bowditch's 

 preparation) were retarded, and its activity brought to a standstill 

 in a short time, when a simple 0*6 per cent solution of NaCl was 

 substituted for the blood or serum. Salt water, therefore, does 

 not in itself contain the whole of the chemical constituents necessary 

 for the maintenance of cardiac activity. 



Merunovics (1877) tried the effect of watery solutions made of 

 the ash, or the alcoholic extract of serum, which, he found, main- 

 tained cardiac activity better than the simple solution of sodium 

 chloride. He attributed this effect to the beneficial action of the 

 alkaline carbonate. 



Stienon (1878), following Merunovics, observed that the 

 difference between the action of the fresh serum and its filtrate, 

 after this had been boiled, consisted in the more limited capacity 

 of the latter to revive a cardiac preparation of which the activity 

 had been reduced to its minimum by prolonged treatment with 

 saline. He also found that neutralisation of the normal alkalinity 

 of the serum with acid diminished its beneficial action on the 

 heart. Lastly, he demonstrated that a solution of sodium chloride 

 rendered alkaline with O'l per cent sodium carbonate is capable of 

 restoring the activity of a heart that had previously been arrested 

 by treatment with salt solution. Gaule, later on, found it more 

 useful for this purpose to add a small quantity of soda instead of 

 the carbonate, pointing out that the alkali is neutralised during 

 cardiac activity by the development of carbonic acid, which converts 

 it into the carbonate. 



Martius (1882) explained the beneficial action of serum by 

 assigning a greater importance to its organic than to its inorganic 

 constituents, and to serum albumin in particular, assuming that 

 the development of cardiac energy was dependent on the presence 

 of some nutrient matter in the circulating fluid. 



Against this positive assumption, however, we must set the 

 work of Ringer, who made a series of experiments to show that 

 the addition of calcic or potassic salts to the NaCl solution 

 effectively prolongs cardiac activity, as has since been confirmed 



