CHAPTER V. 



PROTEINS: THEIR CLASSIFICATION AND 

 PROPERTIES. 



FROM what has already been said in Chapter IV, regarding the 

 protein substances it will be recognized that the grouping of the 

 diverse forms of this class of substances in a logical manner is not 

 an easy task. The fats and carbohydrates may be classified upon 

 the fundamental principles of their stereo-chemical relationships 

 whereas such a system of classification in the case of the proteins 

 is absolutely impossible since, as we have already stated, the mole- 

 cular structure of these complex substances is unknown. Because 

 of the diversity of standpoint from which the proteins may be 

 viewed, relative to their grouping in the form of a logically classified 

 series, it is obvious that there is an opportunity for the presen- 

 tation of classifications of a widely divergent character. The fact 

 that there were until recently at least a dozen different classifica- 

 tions which were recognized by various groups of English-speaking 

 investigators, emphasizes the difficulties in the way of the individual 

 or individuals who would offer a classification which should merit 

 universal adoption. Realizing the great handicap and disadvantage 

 which the great diversity of the protein classifications was forcing 

 upon the workers in this field the British Medical Association re- 

 cently drafted a classification which appealed to that body of scien- 

 tists as fulfilling all requirements and presented it for the consid- 

 eration of the American Physiological Society and the American 

 Society of Biological Chemists. The outcome of this has been that 

 there are now only two protein classifications which are recognized 

 by English-speaking scientists, one the British Classification the other 

 the American Classification. These classifications are very similar 

 and doubtless will ultimately be merged into a single classification. 

 In our consideration of the proteins we shall conform in all de- 

 tails to the American Classification. In this connection we will say," 

 however, that we feel that the British Medical Association has 

 strong grounds for preferring the use of the term scleroproteins for 

 albuminoids and chromo proteins for haemoglobins. The two classi- 

 fications are as follows : 



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