22 PFLUGER'S VIEWS ON THE PROTEIDS. [BK. i., CH. i. 



white of egg, and that which forms part of the living cell. The 

 former may be kept for years, the latter is continually decomposing 

 without any influence from without being necessarily exerted upon it. 



The proteids which we consume as food are indifferent to neutral 

 oxygen ; so soon as they are taken up by organized cells they change 

 their character, by changing the structure of their molecules, and are 

 now subject to the influence of oxygen. The molecule of albumin 

 begins to live by breathing oxygen. 



How thoroughly independent of an immediate supply of oxygen 

 very complex animal processes may be, which are essentially asso- 

 ciated with the metabolism of cell protoplasm, is, however, shewn by 

 certain remarkable experiments in which Pfluger introduced living 

 frogs into chambers containing no oxygen, and the temperature of 

 which was kept low, and observed that for many hours all the processes 

 of the organism continued to be performed. 



How can we explain the immensely increased instability of 

 the living protoplasmic proteid matter as contrasted with non-living 

 proteid matter? 



The assimilation of proteid matter is looked upon by Pfluger as 

 due to the formation of ether-like combinations between the proteid 

 of the cell protoplasm, and the proteid which serves as its food, water 

 being eliminated. In this process a living proteid molecule may 

 bind to itself a non-living, but isomeric, proteid molecule, and this 

 process of polymerism may be conceived to go on almost indefinitely, 

 so that a large and heavy mass may be produced out of, and yet 

 continue to exist as, a simple molecule 1 . 



Pfluger inclines to the belief that in this process of assimilation by 

 the cell, proteid matter undergoes a change in its constitution, the 

 nitrogen passing from the state in which it exists in amides to the 

 more unstable condition in which it exists in cyanogen and its 

 compounds. In this way Pfluger explains why it is that in uric acid, 

 as in many other products of proteid metabolism creatine, guanine, 

 &c. cyanogen radicals are contained, whilst none of these decompo- 

 sition products are to be obtained from non-living proteids. 



Bodies (so -"- n concluding this sketch of the proteids, it must be 

 called Albu- mentioned that there occur in the epithelial and con- 

 minoid) re- nective tissues of the organism certain bodies which 

 lated to the have somewhat close relationship to the proteids, but 

 which are nevertheless distinct from them ; these are 

 chondrin, collagen and gelatin, mucin, elastin, keratin. They will be 

 considered in detail in future sections of this work. 



1 The Author understaiids Pfluger to say that the same constituent atoms or groups 

 of atoms (radicals) mhst be present in different proteids : that the difference is caused 

 either by the final molecule being a different multiple of the same group or groups of 

 atoms (polymerism) or by the oxygen or nitrogen occupying different relative positions 

 with respect to groups of atoms which they serve to link together (metamerism), or by 

 differences in the relative position of groups of atoms or their constituent parts with 

 respect to one another (general isomerism). 



