INTRODUCTION. 



The extraordinarily large number of researches suggested by the hy- 

 pothesis stated in the Preface are so vast in their scope as to enter every 

 domain of the science of living matter, normal and abnormal ; and they are 

 so diversified and exacting in their technical requirements that at the out- 

 set of our work we realized the necessity, for the time being, of limiting 

 our studies by means of practically a single method of investigation and 

 to a single substance. The crystallographic method was selected, for the 

 reasons stated; and one of the proteins was selected because these sub- 

 stances are universally recognized as constituting the most important class 

 of the body constituents, and also because it would seem that modifications 

 in their molecules would be more likely to occur and to be of a more far- 

 reaching influence and importance than in those of other vital substances. 

 Unfortunately, however, the study of the chemistry of proteins has proven 

 so extraordinarily abstruse that our knowledge is still in an early formative 

 stage. It has only been within very recent years that any really important 

 progress has been made; and notwithstanding a large amount of laboratory 

 investigation and the accumulation of a voluminous literature, our informa- 

 tion is still largely of a rudimentary and fragmentary nature. 



The undeveloped state of the science of proteins is perhaps nowhere 

 more evident than in the absence of any classification that seems to be 

 other than of a purely tentative character, in the absence of satisfactory 

 knowledge of such fundamental subjects as the molecular constitution of even 

 the best-known proteins, and in our very incomplete data of the primary 

 dissociation products. The methods of analysis of proteins into the primary 

 dissociation products are not only not strictly quantitative, but also very 

 imperfect qualitatively. The figures of different investigators for a given 

 protein often differ quite as much as for different substances, and there are 

 yet large percentages to be accounted for, such as 30 per cent of globin, 

 74 per cent of egg albumin, 57 per cent of serum albumin, 55 per cent of 

 serum globulin and of fibrin, 59 per cent of lactalbumin, 83 to 90 per cent 

 of proteoses, 39 to 54 per cent of plant globulins, 40 to 65 per cent of glute- 

 lins, 25 to 50 per cent of gliadins, etc. In fact, only one of the proteins, 

 salmine, which is one of the simplest, has been fully accounted for, but even 

 here the data are unsatisfactory, chiefly because a larger per cent (110.5) has 

 been recorded than can exist; Abderhalden found leucin and alanin, which 

 is not admitted by Kossel and Dakin; and there is doubt as to the purity 

 of the substance analyzed, there being several similar bodies in the sper- 

 matozoa of the same species. The data in regard to the other protamines 

 are very incomplete, almost wholly qualitative, and by no means conclusive. 



Whether or not the corresponding proteins of different species of 

 animals or of plants are chemically identical had not, up to the inception 



