1. None of the extracts examined are very potent in small doses. A noticeable effect, however, is produced upon the blood pressure by the extract of fifteen milligrams of shark testis.
2. A small dose of a five per cent. shark testis extract seems to show more pressor action than a larger dose of the same solution.
3. The fall of blood-pressure is due to a vaso-dilation.
4. After repeated (seven or eight) injections of almost any extract, an injection of more of the same extract, or of another extract, which would be rather potent as a "first" injection, causes very little if any response from the blood-pressure.
5. Continued boiling of an extract destroys the pressor substance.
6. The depressor action is then very pronounced and especially prolonged.
7. The depressor substance will dialyze.
8. The pressor and depressor substances cannot be separated by dialysis, because in the repeated sterilizations the pressor substance disappears.
9. The pressor and depressor substances cannot be separated by absolute alcohol, as each seems to be soluble. The solubility is not, however, very great, at least in the cold.
10. It seems impossible to separate the pressor and depressor substances by means of a difference in solubility in cold physiological salt solution, since the depressor substance is even more soluble in that solution than the pressor. And yet the depressor substance is not nearly all removed by this means, even though it is allowed to stand for some time.
11. After cutting the vagi, the recovery from the effect of the depressor substance is much more rapid than with the vagi intact. The amount of fall of blood-pressure is about equal in either case.
12. Extracts of the testis and pancreas of shark; of the testis and spleen of swordfish; and the spiral valve of dogfish show the presence of a pressor substance.
13. Extracts of the testis, spleen, pancreas and liver of shark; of the testis, liver, spleen and kidney of swordfish, and the spiral valve of dogfish show the presence of a depressor substance.
14. Extracts of shark ovary gave no result. I believe, however, that if sufficient of the parenchymatous tissue of the ovary had been obtained a result would have been given by this organ also.