DIGESTIVE ACTIVITY OF MESENCHYME. IOI 



of the thickness of the fin) the animals did not show uneasiness 

 from the effect of the operation. Hemorrhages could not be 

 avoided during injection, but those specimens in which hemor- 

 rhage could be macroscopically discerned were eliminated. Ob- 

 servations in vivo were occasionally made and a large number of 

 fixed tadpoles at different stages after injection were secured. 

 The animals were allowed to live from 2 hours to 3 or 4 weeks 

 after the injection. 



The first set of experiments, of which a report is given in the 

 present paper, consisted in injecting various amounts of edestin. 

 This substance, insoluble in water, appears macroscopically in 

 the form of minute particles, irregular in shape, rather uniform 

 and rarely exceeding in size the eosinophilic granules of leuco- 

 cytes. Every edestin granule ingested by cells can easily be 

 identified in an eozin-azur preparation after Zenker-formol fixa- 

 tion, the granules staining a brilliant red. 



We wish to express to Professor Gies our great indebtedness 

 for chemically purifying this substance. 



Structure of the Dorsal Fin of a Tadpole Tail. A short de- 

 scription of the structure of the edge of the tadpole tail is neces- 

 sary in order to know what kind of cells will be in immediate 

 contact with the substance introduced into it. It consists of 

 a plate of loose mesenchyme covered on both its surfaces by 

 epidermis. The epidermis contains three differently organized 

 layers of cells, all of them exhibiting frequent mitoses. The su- 

 perficial layer of cuboidal epithelial cells is covered by a thin 

 cuticular border. The basal layer of epithelial cells consists of 

 characteristic cuboidal and columnar cells containing sharply 

 defined filaments. The middle layer of the epidermis consists 

 of pigmented cells with peculiarly incurved nuclei. Chromato- 

 phores in the form of many branched cells are not infrequently 

 found in this layer. The epidermis is lined by a heavy basal 

 membrane. Numerous white fibers traverse the tissue between 

 the two basal membranes. 



The loose tissue of the plate contains scattered mesenchymal 

 cells and vessels, a few strands of smooth muscle tissue and nerves. 

 No wandering cells of any kind are normally present in this 



