BEHAVIOR OF ANURA TOWARD COLLOIDAL DYES 25 



8. EXPERIMENTS TO DETERMINE THE PORTAL OF ENTRY OF 



THE DYE 



In all of the preceding experiments the method employed of 

 immersing the larvae and adults in solutions of dye, does not 

 permit us to determine definitely how the dye gains admission 

 to the body. As dye is taken into the alimentary canal through 

 the mouth in such cases, there is an equal opportunity for it to 

 pass through the intestinal mucosa as through the integument. 



Wislocki ('16 a, p. 128) believes it gains admission to the body 

 in the larvae of Rana through the alimentary canal and speaks as 

 follows on this question: 



Study of the sections seems to show conclusively that the epidermis 

 does not serve as a portal of entry for the dye, since there are no visible 

 traces of trypan-blue within or between the cells of this tissue. It seems 

 more probable that the stain gains admission to the body through the 

 alimentary canal, because in certain regions of the gut, the entire intes- 

 tinal mucosa and submucosa are colored a deep diffuse blue and occa- 

 sionally definite granules of dye are distinguishable in these layers. The 

 embryonic intestine behaves radically differently towards the dye than 

 does that of the adult, which under no circumstance, has been known to 

 absorb the dye or to have visible particles of stain in the cells of the 

 mucosa. 



The experiments of Overton ('04) and Maxwell ('13) point to 

 the conclusion that there is a constant flow of water through the 

 skin in the case of a frog immersed in water and that the excess 

 of water is eliminated by the kidneys. It has been stated, accord- 

 ing to Bayliss ('15, p. 356), that the urine secreted by a frog in 

 twenty-four hours may exceed the total weight of the body. After 

 the water has passed through the skin Volhard ('12) has shown 

 that it is conveyed to the general circulation by the lymphatics. 

 The experiments of Moore ('15) also point to the fact that the 

 water is taken up by the veins as well as by the lymphatics. 

 Be this as it may, it is an assured fact that water passes through 

 the frog's skin in accordance with the laws of osmosis, and that it 

 reaches the general circulation from the intercellular tissue 

 spaces by way of the lymphatics. 



By means of two sets of experiments, the writer has been able 

 to determine definitely the portal of entry of the dye in both 



