HYDE: EXPERIMENTS ON THE SKATE. 63 



pages discloses the fact that increased force of cardiac activity 

 is usually accompanied by increased force of respiratory ac- 

 tion and blood pressure. But NH4CL m/8, urea, and Na2HP04 

 are exceptions. NH4CI increases blood pressure without in- 

 creasing cardiac force. Urea produced increased force of re- 

 spiratory and cardiac activity without raising blood pressure, 

 and Na2HP04 m/8 increases force of cardiac but decreases 

 force of respiratory action. Moreover, most of the salt solu- 

 tions of a definite concentration that augmented the force of 

 cardiac also increased the force of the respiratory rhythm and 

 proved either indifferent or depressing in their influence upon 

 the rate of both of these activities. 



The exceptions are MgS04 m/8, which stimulates force of 

 cardiac but not that of respiratory activities and is depressing 

 to rate, and NaOH m/8, that stimulates cardiac force and rate 

 but not the respiratory rhythm. 



The toxic effect of many solutions at certain concentrations 

 was counteracted by definite strengths of other salts. Of these 

 antagonistic solutions, CaCk m/32 or m/8 proved most ex- 

 tensively favorable. It was interesting to learn that certain 

 concentrations of some salt solutions prolong the cardiac sys- 

 tole and the inspiratory phases, while other solutions favor 

 diastolic and expiratory phases. M/2 NaCl and also m% 

 CaCk prolong systole and inspiration, while KCl m/8, NaH2 

 PO4 m/8 prolong inspiratory activity and diastole. Moreover, 

 strong solutions of MgS04, NH4CI and BaCk prolong diastole 

 and expiratory activity. 



The salts that were especially depressing upon the cardiac 

 and respiratory phases were KCl and MgS04. There are cer- 

 tain optimum per cents of salts and acid solutions, below or 

 weaker than which the effect is stimulating or initiates tempo- 

 rarily increased activity, and above or greater concentration 

 than which the solution inhibits or decreases activity or proves 

 toxic. Moreover, increased olood pressure, as a rule, is accom- 

 panied by a decrease in rate of cardiac and respiratory activity. 



■I-Univ. Sci. Bull . Vol. V. No. 4. 



