238 Charles G. Rogers. 



soon discarded. The first consisted in carefully isolating the 

 hearts in watch glasses, each containing about ten cc. of the 

 solution to be tested, and making observations upon the number 

 and quality of the beats developed. This method was employed 

 only during the early stages of the work as it did not permit of any 

 accurate estimate of the amount of work done by the heart. The 

 second method was that of carefully suspending the hearts by 

 means of delicate glass hooks in connection with light recording 

 levers and allowing them to trace upon smoked papers the records 

 of their contractions. In these experiments the hearts were 

 moistened with the solutions by means of camel's hair brushes. 

 Oxygen, of course, is easily taken up from the air, but the effects 

 of the various constituents of the solutions are difficult to deter- 

 mine with this method as the amount of solution in contact with 

 the heart is small and variable. One can not be sure at any given 

 time that the solution has replaced the body liquid normally 

 present. In view of this fact a third method was employed. 

 This was similar to the second except that the hearts were im- 

 mersed in tubes, each containing about 30 cc. of the solution. 

 While the general results of the first method agree with those of 

 the third they are disregarded in the final summing up of the 

 work as lackmg m sufficient accuracy. The second method 

 failed to give uniform results. The author feels that the results 

 obtained by the third method are far more reliable than those 

 obtained by either of the preceding ones, hence they form the 

 basis of the following report. 



EXPERIMENTS. 



A. What IS the Opttnnun Concentration of Salt Solution u'hich 

 will Favor the Rhythmic Activity of the Heartt 



Botazzi^ has measured cryoscopically the osmotic pressure of 

 the blood of many of the marine invertebrates and has found that 

 it is practically the same as that of the sea water. The average 

 depression of the freezing point in the body liquids of inverte- 

 brates is given by Hamburger'- as — 2°. 29, and the depression of 

 the freezing point of the sea water is given by Hober as — 2°. 3. 



'Botazzi. Archives Italiennes de Biologic, xxviii, 1897, p. 67. 



"Hamburger. Osmotischer Druck und lonenlehrt* in den Medicinischen Wissenschaften. 



