BEHAVIOR OF ANURA TOWARD COLLOIDAL DYES 57 



In comparing the above observations with conditions which 

 might normally occur, we must take into consideration the un- 

 usual environment in which development has taken place. Be 

 this as it may, we are able to obtain an approximate estimate of the 

 time at which the renal organs first begin to function in the ca- 

 pacity of eliminating waste material from the circulation. We 

 can therefore state that dye granules may make their first appear- 

 ance in the pronephros of toad larvae on the ninth day (p. 13), 

 in the right mesonephros on the tenth day and in the left mesone- 

 phros on the fifteenth day after fertilization. The presence of 

 dye granules would at least indicate that the functional activity 

 of these organs has only quite recently been established. 



One of the most striking features observed in a study of adult 

 and larval tissues, is the apparent inequality in the ability of cells 

 of exactly the same type to store the dye. Attention has already 

 been drawn to this by Hektoen ('11), Rosenow ('06) and others. 



It is not unusual in toad larvae to find an endothelial cell of the 

 lymphatic or venous systems which is loaded with dye granules to 

 be lying contiguous to another cell of the same type in which not 

 a trace of dye is present. Corresponding observations can be 

 made for the stellate cells of the liver capillaries. Equally strik- 

 ing is the presence of free cells loaded with dye granules which lie 

 in the tissues side by side with exactly similar types of free cells 

 in which no dye granules are present. At the same time, as has 

 been so uniformly observed by all investigators, white blood- 

 corpuscles containing dye granules are rarely found in the cir- 

 culating blood and not to any extent, even after larvae have 

 experienced a prolonged immersion in dye- The explanation of 

 this latter phenomenon has, as we know, been one of the mooted 

 questions Without pretending to furnish any final solution to 

 the problem a few observations recently made by the writer may 

 be of interest in this connection. 



Downey ('17a) has recently shown that cells which do not 

 ordinarily take up the dye in the circulation, as polymorpho- 

 nuclears and lymphocytes, may be made to do so by isolating 

 them in a segment of the femoral vein which has been doubly 

 ligatured and into which, between the ligatures, a 1 per cent 



