114 MAN --AN ADAPTIVE MECHANISM 



If the mechanism of blood coagulation was evolved 

 through the biologic exigency of hemorrhage, usually 

 from wounds received in combat, then according to the 

 law of phylogenetic association, we should conclude 

 that the areas most exposed phylogenetically to injury 

 would be more fully equipped with the elements for coagu- 

 lation than the more protected regions. In other words, 

 we should expect to find that the inner parts, less 

 frequently subject to laceration, would show a higher 

 tendency to protracted hemorrhage than do the com- 

 monly exposed areas of the surface and the extremities. 

 Clinically, we know that in general this is true ; that 

 the quick coagulation of blood in the superficial tissues 

 skin, subcutaneous tissues and muscles is in sharp 

 contrast to the slow coagulation in the protected fields. 

 The mucous membrane of the frequently wounded 

 mouth bleeds slowly and heals quickly. On the other 

 hand, the mucous membranes of the stomach and intes- 

 tines, of the bladder, of the fallopian tubes and of the 

 respiratory tract show a tendency to bleed indefinitely. 

 Limbs may be crushed and torn, evulsed even, with 

 less hemorrhage than is caused by a slight abrasion of 

 the mucous membrane of the intestines. 



It may be argued that the quick coagulation in ex- 

 ternal tissues is due to contact with oxygen. How, 

 then, would one account for the fact that bleeding in 

 subcutaneous wounds, where there is no supply of oxy- 

 gen, is arrested with equal promptness? The exten- 

 sive laceration of blood-vessels in childbirth is quickly 

 overcome, whereas nose-bleed, with all the advantages 

 of air contact, may persist stubbornly, and operations 

 on the tonsil, where there is an ample supply of air, 



