i v PREFACE. 



about all of those differences which serve to characterize genera, species, 

 and individuals. Furthermore, since the factors which give rise to consti- 

 tutional changes in one vital substance would probably operate at the same 

 time to cause related changes in certain others, the alterations in one may 

 logically be assumed to serve as a common index of all. 



In accordance with the foregoing statement it can readily be under- 

 stood how environment, for instance, might so affect the individual's meta- 

 bolic processes as to give rise to modifications of the constitutions of certain 

 corresponding proteins and other vital molecules which, even though they be 

 of too subtle a character for the chemist to detect by his present methods, 

 may nevertheless be sufficient to cause not only physiological and morpho- 

 logical differentiations in the individual, but also become manifested physio- 

 logically and morphologically in the offspring. 



Furthermore, if the corresponding proteins and other complex organic 

 structural units of the different forms of protoplasm are not identical in 

 chemical constitution it would seem to follow, as a corollary, that the 

 homologous organic metabolites should have specific dependent differ- 

 ences. If this be so it is obvious that such differences should constitute a 

 preeminently important means of determining the structural and physio- 

 logical peculiarities of protoplasm. 



It was such germinal thoughts that led to the present research, which 

 I began upon the hypothesis that if it should be found that corresponding 

 vital substances are not identical, the alterations in one would doubtless be 

 associated with related changes in others, and that if definite relationships 

 could be shown to exist between these differences and peculiarities of the 

 living organism, a fundamental principle of the utmost importance would be 

 established in the explanation of heredity ,'mutations, the influences of food 

 and environment, the differentiation of sex, and other great problems of 

 biology, normal and pathological. 



To what extent this hypothesis is well founded may be judged from 

 this partial report of the results of our investigations: It has been conclu- 

 sively shown not only that corresponding hemoglobins are not identical, but 

 also that their peculiarities are of positive generic specificity, and even much 

 more sensitive in their differentiations than the " zooprecipitin test. " More- 

 over, it has been found that one can with some certainty predict by these 

 peculiarities, without previous knowledge of the species from which the hemo- 

 globins were derived, whether or not interbreeding is probable or possible, 

 and also certain characteristics of habit, etc., as will be seen by the context. 

 The question of interbreeding has, for instance, seemed perfectly clear in 

 the case of Canute and Muridoe, and no difficulty was experienced in 

 forecasting similarities and dissimilarities of habit in Sciuridce, Muridoe, 

 Felidce, etc., not because hemoglobin is per se the determining factor, but 

 because, according to this hypothesis, it serves as an index (gross though 

 it be, with our present very limited knowledge) of those physico-chemical 

 properties which serve directly or indirectly to differentiate genera, species, 

 and individuals. In other words, vital peculiarities may be resolved to a 

 physico-chemical basis. 



EDWARD TYSON REICHERT. 



