6 CHAKLES F. W. McCLURE 



agent and alcohols, and stains some of the tissues a deep and 

 diffuse blue. In larvae so treated not a trace of dye will ordinarily 

 be found in any of the tissues, except that which has actually 

 been stored in the form of dye granules in the cytoplasm of the 

 cell. In experimental larvae which have remained in tap water for 

 several weeks before killing, dye granules may still be found 

 stored in the cytoplasm of typical cells. 



Serial sections were made of three hundred and forty toad and 

 frog larvae. These cover all of the critical stages before, as well as 

 after definite reactions of the tissues toward the dye, in the form 

 of dye granules, can be observed. Serial sections were also made 

 of one hundred and ninety different tissues and organs of advanced 

 larvae and adult amphibians which had been subjected to a 

 treatment of dye. 2 



As fixing agents, a 10 per cent solution of neutral formalin 

 and Bouin's fluid were almost exclusively used. A careful com- 

 parison of the tissues fixed by these two methods shows that dye 

 granules remain unchanged in both cases and as originally 

 deposited in the living cell. The only difference which results 

 in the use of Bouin's fluid for the fixation of amphibian larvae 

 lies, as far as I can determine, in the more perfect fixation of 

 the cells. 



Most of the larvae were stained in toto with borax-carmine. 

 Mayer's alum-carmine and a 1 per cent aqueous solution of 

 Bismarck brown were used for staining on the slide. A counter 

 stain of eosin proved serviceable in some cases, and controls were 

 often stained with Reagan's ('14) modification of Mann's methyl 

 blue-eosin stain. 



Observations were frequently made on larvae which had re- 

 mained in dye solutions, to determine the rapidity and extent to 

 which the lymphatics of the caudal fin had stored the dye. These 

 observations were made in the usual manner with high power 

 objectives on living larvae placed in a micro-aquarium. In 

 Spalteholz preparations of the caudal fin in which the endothelium 



1 All serial sections of larvae and of other tissues studied in connection with this 

 investigation were prepared by iny assistant Miss Grace Lloyd, to whom my 

 thanks are due. 



