116 MAN --AN ADAPTIVE MECHANISM 



method, using extracts of tissues taken from those 

 parts of the body, which, clinically, show differences 

 in the coagulation times. In these experiments tissues 

 were taken from the brain, the skin, the skeletal 

 muscles, the buccal mucous membrane, the lungs, the 

 pancreas, the deep lumbar muscles, the heart muscle, 

 the intestinal mucosa, the thyroid and the kidney. 

 Although the data are insufficient to be conclusive, 

 the results recorded are in keeping with clinical obser- 

 vations. That is, the quantity of thromboplastin in 

 the skin and in the muscles was, in general, greater 

 than in the pancreas, the deep lumbar muscles and 

 the intestinal mucosa. These facts point to the conclu- 

 sion that the distribution of thromboplastin through- 

 out the body, like the distribution of contact ceptors 

 and of the mechanisms for combating pyogenic infec- 

 tion, has been determined by the past experience of 

 the species and by the relentless laws governing the 

 survival of the fittest. 



Acidity and Respiration 



Among other chemical mechanisms which have been 

 evolved for a specific purpose are the cerebral mecha- 

 nisms for the maintenance of the normal alkalinity of 

 the blood and the chemical purity of the body. The 

 most important receptor mechanism for the mainte- 

 nance of the normal alkalescence is the respiratory center 

 in the medulla, which is governed by the H-ion con- 

 centration 1 and possibly in part by the oxygen content 



1 The alkalinity or acidity of a fluid depends upon the number of free 

 OH or H-ions it contains, an ion being an electrical molecule. The 

 degree of acidity of a fluid, therefore, may be determined by measur- 

 ing the hydrogen ions it contains, i.e., its H-ion concentration. 



