REACTION OF SELACHII TO INJECTIONS 127 



been argued, because, an equilibrium having been established, all 

 urea formed would need to be eliminated. Hence if theie is 

 little urea excreted it is because relatively little is formed. The 

 limited excretion of urea in the urine is dependent upon the 

 metabolism, which must proceed at a slow rafe in these forms, 

 and also upon the amount of urea excreted in the bile. 



MacCallum, in the 1917 Herter Lectures in New York, stated 

 that the selachians entered the sea when its salt concentration 

 was less than it now is and that as the sea became concentrated 

 the selachians retained more and more urea in the blood to 

 keep it isotonic with the sea-water. 



We found that the dogfish kidney is able to excrete injected 

 solutions quite as rapidly as the mammalian kidney and hence 

 the inefficiency of the former is not one of rate of excretion, but 

 of amount and of inability to eliminate certain kinds of sub- 

 stance. Non-toxic solutions of all kinds when injected into the 

 muscles of the body wall appeared in the urine in fourteen or 

 fifteen minutes, and when injected intravenously^ appeared in 

 the urine in about eight minutes. In this rate the dogfish com- 

 pares favorably with mammals (Rowntree and Geraghty, '12). 

 The dogfish kidney would probably eliminate all of an injected 

 solution in time, if it were not for the fact that the liver quickly 

 eliminates the larger part of it. The liver is many times larger 

 than the kidneys and has taken over much of the excretory 

 function. As noted above, when pheno-sulphonepthalein was 

 injected, the liver excreted in a given time more than twice as 

 much of it as did the kidneys, and in concentration many times 

 greater. However, the difference in amount excreted by the 

 two organs was less than the relative difference in size by which 

 the liver surpasses the kidney. 



Colored solutions stained the posterior part of the kidney 

 more intensely than the anterior end, thus demonstrating the 

 fact that in the former the excretory function is better developed 

 than in the anterior or sexual (Felix, '12) end. The anterior 

 region is able to excrete some part of solutions injected, so it is 

 not entirely devoid of excretory function, as some investigators 

 have believed. This point should be studied further. The 



