08 ANNALS NEW YORK ACADEMY OF i^CIENCES 



rule are swollen, a small number burst. In the swollen state it is possible 

 that their oxygenating function is interfered with. This would also 

 partially explain the effect on respiration. 



At death in fresh water, the plasma is deficient in urea. Baglioni and 

 Mines have shown that urea is a necessary ingredient of the selachian 

 blood for the maintenance of normal cardiac activities. Baglioni con- 

 cluded that it promoted systolic tonus. He found that other substances, 

 such as cane sugar, cannot replace it, and that therefore urea is necessary 

 for its chemical effect on heart tissue rather than for its osmotic contri- 

 bution. 



The deficiency of the blood in salts, however, is greater than in urea. 

 Baglioni concluded that the sodium salts increase diastolic tonus. He 

 found that an equal increase in urea and sodium chloride causes an in- 

 crease in systolic and diastolic tonus up to a certain point beyond which 

 cardiac activities come to a standstill. He concluded that in the propor- 

 tions in which the salts are found in the blood, systolic tonus counter- 

 acted diastolic tonus and the interaction of the two was necessary for 

 normal rhythmical contraction. It has been shown in the present paper 

 that the balance normally present between these two substances is upset, 

 for the blood is losing salts more rapidly than its urea. Loeb ('11) has 

 called attention to the role of the salts of sodium, potassium, calcium and 

 magnesium in the preservation of life. He has maintained the impor- 

 tance of the proportion in which they exist in sea-water. The same pro- 

 portion of the same salts has been found by Macallum ('10) in the blood 

 of animals representing different phyla. It has been shown in the pres- 

 ent paper that the salts diffuse out through the gill membranes, and it is 

 possible that the different ions pass out at different rates. Thus the 

 sodium and magnesium ions may pass out first of all because of their 

 speed of diffusion, and the potassium and calcium may pass out to a 

 smaller extent and later. Thus the normal relations of these ions so 

 necessary to the normal heart beat and to the activities of all tissues may 

 be thus changed. A more rapid loss of salts on the part of the blood than 

 on the part of the tissues leads to a disparity between the osmotic pres- 

 sures of the two. The tissues absorb water, as shown, leading to an 

 oedema. This interferes with their normal action — as, for example, the 

 water rigor of muscle. 



The marine invertebrates, because of the lack of a quickly acting regu- 

 lative mechanism, are helpless in the event of a rapid change in the 

 molecular concentration of the external medium. Though their range 

 of movement is more restricted than that of the fishes, yet a regulative 

 mechanism must have been developed in the case of those forms which 



