While most specimens of dog semen shorten the coagulation time of blood because of their thromboplastic activity, certain specimens render blood incoagulable or delay coagulation; in contrast to human semen, this adverse effect on coagulation is not overcome with calcium ions and is due to a different mechanism, the lysis of fibrinogen. The citrate content of dog prostatic fluid is small.

Human semen which has become liquefied does not contain thrombin or prothrombin, but fibrinogen and thromboplastic substances are present. Beef fibrinogen added to semen is destroyed by incubation for 18 hours, but added prothrombin and thromboplastic substances are still present after this treatment. Dog semen, in some instances, contains small amounts of thrombin.

The semens of man and dog contain a fibrinolysin for human blood which seems not to differ greatly from the fibrinolysin associated with hemolytic streptococci. The blood of the donor of prostatic fluid is susceptible to fibrinolysis by this fluid. However, the blood of persons with some diseases, is absolutely resistant to the action of seminal fibrinolysin. In how many diseases this happens has not yet been determined.

The semens of man and dog both contain an agent capable of inactivating fibrinogen, but in different amounts. This activity may be called fibrinogenase. Human semen is rich in fibrinolysin, poor in fibrinogenase; dog semen is rich in fibrinogenase, poor in fibrinolysin. These species differences, together with the fact that it is easy by appropriate dilution to retain the stronger proteolytic agent and eliminate the weaker one, imply that fibrinolysin and fibrinogenase are different entities.

Dog semen, and less constantly human semen, contain very small amounts of trypsin.

All of these proteolytic agents derive from the prostate gland; their secretion in prostatic fluid constitutes a hitherto undescribed function for the prostate gland.