REACTION OF SELACHII TO INJECTIONS 115 



/. Gills. The sinuses which intervene between the arterial 

 arches and the capillaries in the filaments, as described in the 

 experiments with carmine, are lined with endothelium very 

 phagocytic to trypan blue. The dye is in greater concentration 

 in these cells than in any others examined. In some sinuses 

 (figs. 3 and 4) every cell is engorged with the dye. Even in the 

 'large artery (fig." 3) a few of .the endothelial cells contain blue 

 granules. In figure 4 the cells and nuclei have rounded. Many 

 are nearly detached or are lying free in the sinus ready to move 

 with the blood stream as circulating phagocytes. Some of the 

 granules in the cells seem to be contained in vacuoles, although 

 the fact is not shown in the drawing. Most of the granules 

 shown are trypan blue, but two cells marked 'a:' contain also 

 some normal black pigment. In some cells the dye completely 

 hides the nucleus. Practically all the sinuses examined are 

 completely lined with cells filled with trypan blue, but a few 

 sinuses are unstained. 



A few cells in the capillaries contain blue granules. The 

 epithelium covering the filaments does not contain trypan blue, 

 although some investigators have suggested that the gills may 

 excrete other substances besides gas. 



3. Excretory toxins 



A. Potassium chromate. 1. An adult dogfish received intra- 

 muscularly 150 mg. per kg. body weight of potassium chromate 

 in a 1 per cent solution. Autopsy was performed after thirty 

 hours and when the animal was moribund. 



The kidneys and spiral valve were greatly congested, the 

 latter containing a bloody fluid. Other organs appeared to be 

 normal at autopsy. 



2. An adult received intramuscularly 75 mg. per kg. body 

 weight of potassium chromate in 1 per cent solution. Autopsy 

 was performed after twenty-four hours while the animal was 

 still active. The amount of toxin injected was less than that 

 which Denis ('14) found to be necessary to kill a dogfish. In 

 this specimen all the organs appeared normal except the spiral 

 valve and kidney, which were slightly congested. 



