NOMENCLATURE 165 



Table I provides a comparison of several of the more commonly 

 used nomenclatures, and indicates the system we shall use in this 

 book. It will be seen that in the nomenclature proposed for general 

 use only two departures are advocated from names previously used, 

 that is, in the use of "hemochrome" and "hem/chrome" in place of 

 "hemochromogen" and "parahematin." The term "hemochromogen" 

 is associated historically with an erroneous conception of one of these 

 substances as the colored component of hemoglobin. These com- 

 pounds are in any case not "chromogens" in the chemical sense, i.e., 

 ieuco compounds. The new term has the additional advantage of 

 greater brevity. 



For general use, the term "base-iron-porphyrins" (e.g., pyridine, 

 ferroprotoporphyrin) for "bemochromes," as required by the Clark- 

 Drabkin nomenclature, is unduly cumbersome. In addition, it 

 excludes substances in which the nature of the organic part is not 

 known with certainty but which are of definite hemochrome nature 

 (e.g., verdohemochromes). 



The terms "hemo-" and "hemi-," denoting, respectively, ferrous 

 and ferric hematin compounds have been used by several workers 

 (e.g., Anson and the school of Heubner) and have more recently been 

 suggested again by Holden (IS 17). Objections have been raised to 

 them on the basis of possible errors of spelling or pronunciation, but 

 these are just as likely to occur with the "ferro"-"ferri" system of 

 Pauling and Barron. For the present, however, it is proposed to 

 italicize the i or o in these words when the state of oxidation of the 

 iron is of importance, to avoid any possibility of error. The term 

 "hemochromes" will occasionally be used as a generic term including 

 hem'tchromes (as has been done elsewhere with "hemochromogen"), 

 in which case the o will not be italicized. 



Whatever nomenclature is used, the prefix indicating the nature 

 of the porphyrin side chains is frequently omitted when these are of 

 the proto type. Thus "hematin" signifies "protohematin." Sub- 

 stances containing different porphyrins will be distinguished by the 

 appropriate prefix; for example "mesohematin" and "coprohematin," 

 signifying the hematins from meso- and coproporphyrin, respectively. 

 In certain cases where the type of porphyrin is of no consequence, 

 and which will be obvious from the context, omission of the prefix 

 will also be made. 



