HEART BEAT OF FRESH WATER ANIMALS. 200, 



pended by passing a hook through the apex below and one 

 through the auricle above. In this way one can obtain a record 

 of both the ventricular and the auricular contractions in their re- 

 lations one to the other. The results of several experiments 

 show that sea water favors the relaxation of the ventricle, while 

 it has either no effect or, a slightly stimulating one upon the aur- 

 icles. The tracings show a more orderly sequence of auricular 

 systole followed by ventricular systole, than in " Ringer," where 

 the auricular systole has a tendency to fuse with the ventricular, 

 owing possibly to incomplete relaxation of the ventricle. The 

 question is being studied further in connection with the effects of 

 magnesium on the heart ; and as this paper is in the nature of a 

 preliminary communication, the discussion of it will be left to a 

 future date. 



As the only practical difference between sea water and " Rin- 

 ger " is the magnesium present in the former, it seems more than 

 likely that the latter salt is responsible for the difference in the 

 effect of these two solutions. As in the case of the marine crab, 

 so in the turtle's heart, sea water rendered isotonic with the blood 

 seems to be an excellent sustaining fluid ; in other words sea 

 water isotonic with the blood is a " physiologically balanced solu- 

 tion " for the turtle's heart. It is conceded that sea water con- 

 tains magnesium in excess of that usually found in blood, and it 

 is for that very reason it has proved useful in pointing the way 

 for further research ; but while it is found in the blood in the 

 proportion of about two of magnesium to three or more of calcium 

 (Hammarsten), the conditions are reversed in muscle and nerve, 

 the proportion being about two of magnesium to one of calcium. 

 One would therefore expect the quantity of magnesium to vary 

 considerably at different times, and it is difficult to say what con- 

 stitutes an excessive amount ; an optimum has yet to be 

 determined. 



In conclusion it should be said that these results were to be 

 expected in the light of those of Quinton, 1 who not only trans- 

 fused dogs with isotonic sea water in quantities equal to the 

 quantity of blood withdrawn, but also injected large quantities 

 intravenously, without serious consequences. " Entre l'eau de 



1 Quinton, R., "L'Eau de Mer Milieu Organique," 1904, p. 160. 



