WITH NATIVE AND DERIVED PROTEINS. HARRIS. 81 



chemical union of oxygen with the haemoglobin which dissoci- 

 ates in the neighbourhood of the living cells owing to the partial 

 pressure of oxygen in them being always zero. In the lung- 

 alveoli, oxygen is not present to more than 15 to 16$ of an 

 atmosphere (that is 104 mm of mercury), and this pressure of 

 itself would be inadequate to drive the oxygen into solution in 

 blood-plasma to an amount sufficient for the respiratory needs 

 of the tissues, hence the blood possesses in its red corpuscles a 

 substance capable of uniting with the inorganic oxygen in such 

 a way that it can carry far more oxygen to the tissues than could 

 ever possibly reach them in solution in a colloidal protein sub- 

 stance like the plasma. It is of advantage to the body that there 

 be formed, therefore, complexes between proteins or protein- 

 derivatives and certain inorganic ions; and Dr. Creigh- 

 ton, 1 by having studied some of these in detail, has thrown a 

 good deal of light on their probable nature. 



The whole of modern medicine is permeated by the notion 

 that bioplasm is affectable, that is, is capable of responding to 

 stimuli, a large number of which are chemical. Thus the 

 formation of an an^-body is only possible because there is a 

 reaction on the part of the affectable living matter to the 

 chemical stimulus of the foreign substance: if toxin be the 

 chemical stimulus, then antitoxin is the chemical response. 

 But the toxin . must first come into chemical union with the 

 protoplasm else no antitoxin can result, just as the food mole- 

 cule must come into chemical relationship with the protoplasm 

 else no food could be absorbed. 



The power of the proteins of blood-serum to absorb or take 

 up either acids or alkalies is of fairly high importance to the 

 bodily health. Thus, confining ourselves to the absorption of 

 acids only, if we add normal acid to blood-serum and use methyl 

 orange as an indicator, we shall have to add 0.18 c. c. of normal 



(N\ 

 -r-j hydrochloric acid to turn the indicator pink. If now we 



titrate, similarly, the saline dialysate from the serum, the acid- 



1. Creighton, H. J M. : loc. cit. 



