496 



PROTOPLASM 



The speed at which blood coagulates varies in different animals. 

 The blood of geese coagulates very slowly, even more slowly 

 than that of hemophiliacs. Glycolysis, or the splitting of glucose 

 into lactic acid, and blood coagulation are coupled reactions; i.e., 

 glycolysis (decrease in sugar or increase in lactic acid) and coagula- 

 tion are rapid in normal men (6 min. for coagulation), slow in 

 hemophilic men (180 min.), and very slow in geese (252 min.). 



We now come to the evident question. Why does blood not 

 coagulate in the body, as it contains all of the four constituents 

 necessary for coagulation? The suggested cause of hemophilia 

 is again a possible answer here, viz., that the platelets do not 

 break down when in the body. It has also been suggested that 

 some substance normally in the blood, and continuously supplied 

 to the blood when in the body — possibly heparin — functions as 

 an anticoagulant. This problem and others, such as the fact 

 that blood does not coagulate when withdrawn into paraffin- 

 coated vessels, remain for future workers to solve. Acidity and 

 alkalinity, so often found to be contributing if not primary causes 

 of physiological processes, apparently are not significant factors 

 in blood coagulation. Eagle and Baumberger find no marked 

 change in pH during the coagulation process. 



Blood coagulation does not appear to rest upon a strictly 

 colloidal property {e.g., instability) such as is responsible for the 

 coagulation of lyophobic suspensions. The question, therefore, 

 arises, What is its physical nature? Little can be said. It is not 

 known whether fibrin (the coagulum) is a product of fibrinogen 

 (the substance coagulated) or whether coagulation involves 

 simply an intramolecular rearrangement. Either of these is 

 possible in the light of our present knowledge. Although still 

 controversial, the bulk of evidence favors the theory that throm- 

 bin is an enzyme activating the transformation, rather than a 

 substance that combines with fibrinogen to form fibrin. 



Natural Anticoagulants. — The clotting of blood is a desirable 

 feature for those whose blood is involved ; but for animals seeking 

 the blood of others, clotting is objectionable. The leech, the 

 vampire bat, and the lamprey feel this way about it. They live 

 upon the blood of animals, the flow of which would stop if they 

 did not have some means of preventing coagulation. The leech 

 and the vampire bat produce a secretion which they pour into 

 the wounds that they make. A secretion from the buccal glands 



