MEMOIR XX VII.] THE EFFECTS OF ALLOTROPISM. 379 



with the utmost facility. Charged with the oxygen it 

 has thus obtained, the arterial blood passes to all parts 

 of the system ; and now arises that striking but all-im- 

 portant physiological fact, that it does not attack indis- 

 criminately all those parts of the soft solids which it first 

 encounters, but, proceeding in a measured w r ay, exerts its 

 action on such particles alone as have become effete, and, 

 accomplishing the great process of interstitial death, re- 

 solves those particles into other forms, so that they can 

 be eliminated from the system by the lungs, the kidneys, 

 and the skin. 



Now why is it that things proceed in this way ? What 

 is it that regulates this interstitial death ? Why is one 

 atom preserved and another surrendered ? 



It is upon these obscure points that the recent discov- 

 eries in allotropism shed a flood of light. 



The three leading neutral nitrogenized bodies, fibrin e, 

 albumen, and caseiue, are characterized by exhibiting al- 

 lotropism in a most remarkable degree, and that in a 

 double sense. 1st. Though so different from one another 

 in their physical and chemical relations, it is admitted 

 on all hands that they are mutually convertible : the al- 

 bumen of the egg, during incubation, gives rise to fibrine 

 and other allied bodies; from caseine in the milk with 

 which the young mammalia are nourished, the albumi- 

 nous and fibrinous constituents of their systems arise; the 

 nurse fed on fibriue and albumen secretes caseine from 

 the mammary gland. Indeed, there is no more. reason 

 to regard these three bodies as essentially distinct sub- 

 stances than there is to apply the same conclusion to 

 charcoal, plumbago, and diamond. Between the two 

 cases there is the most complete analogy; and if char- 

 coal, plumbago, and diamond are merely allotropic forms 

 of one substance, the same holds good for fibrine, albu- 

 men, and caseine. But, 2d, each of these three com- 



