50 CHARLES F. W. McCLUEE 



Intravenous injections of embryos at a time prior to the estab- 

 lishment of a lymph flow between the periphery and veins, might 

 also lead to interesting observations regarding the functional 

 state of the renal epithelium, as well as that of other tissues at such 

 a tune. Such experiments would be analogous to cases in which 

 dye might be absorbed by the intestinal mucosa before the lymph 

 flow was established between the periphery and the veins. 



On the fifth day the intestinal canal of the toad larva is filled 

 with yolk which would make it impossible for dye to pass through. 

 No dye was observed in the intestinal canal of the living larvae 

 until the seventh day, although conditions were such that it would 

 have been possible for dye to pass through sometime between the 

 fifth and sixth days. At the time when a continuous lymph flow 

 is first established through the lymphatics between the tissue 

 spaces and the veins, it is therefore not impossible that dye may 

 at the same time gain admission to the body through the intes- 

 tinal mucosa or may be taken up directly by the veins (Moore, 

 '15). Irrespective of the possibility that dye may also reach the 

 general circulation by a route other than by the lymphatics, it is 

 clearly evident that it does not do so until a continuous lymph 

 flow is established through the lymphatics between the tissue 

 spaces and the veins. 



12. DOES THE METHOD OF VITAL STAINING BY COLLOIDAL ACID 



DYES CONTRIBUTE ANY EVIDENCE IN FAVOR OF THE VIEW 



THAT THE LYMPHATICS ARE DERIVED FROM THE VEINS? 



Regarding the view that lymphatics are derived from the endo- 

 thelium of the veins, Wislocki ('16 a, p. 127) states as follows: 



Three views have assumed the most important places among the 

 numbers of theories which have been evolved to explain the develop- 

 ment of new lymphatic vessels. 



1 . That lymphatics may result from a transformation of blood-vessels, 

 and that extension of the lymphatic system results from the coupling 

 on or addition of these changed blood-channels. 



2. That the endothelial cells of the lymphatics may arise from cells 

 of the extra-vascular mesenchyme. 



3. That after the initial outgrowth of lymphatics from the veins, in 

 the form of lymph-hearts has occurred, neither mesenchyme cell nor 

 blood-vessel endothelium contributes any further to their growth; but 



