294 BIOLOGY: GENERAL AND MEDICAL 



may each have only a fraction of this number, it can readily be 

 conceived how, primarily by differences in chemical constitution 

 of vital substances and secondarily by differences in chemical 

 composition, there might be brought about all those differences 

 which serve to characterize genera, species, and individuals. 

 Furthermore, since the factors which give rise to constitutional 

 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 

 understood how environment, for instance, might so affect the 

 individual's metabolic 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 morphological 

 differentiations in the individual, but also become manifested 

 physiologically 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 differences. If this be so, it is obvious that 

 such differences should constitute a pre-eminently important 

 means of determining the structural and physiological peculiarities 

 of protoplasm." 



"To what extent this hypothesis is well-founded may be judged 

 from this partial report of the results of our investigation: It 

 has been conclusively shown not only that corresponding hemo- 

 globins are not identical, but also that their peculiarities are of a 

 positive generic specificity, and even much more sensitive in their 

 differentiations than the " zooprecipitin test." Moreover, it has 

 been found that one can with some certainty predict by these 

 peculiarities, without previous knowledge of the species from which 

 the hemoglobins were derived, whether or not interbreeding is 

 probable or possible, and also certain characteristics of habit, etc." 



"The question of interbreeding has, for instance, seemed 

 perfectly clear in the case of Canidce and Muridce, and no difficulty 

 was experienced in forecasting similarities and dissimilarities of 

 habit in Sciuridoe, Muridce, Felidce, etc., not because it 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." 



Though it is naturally much more difficult to deter- 

 mine with reference to the cells, there are reasons for 

 believing that the cell juices, like the body juices, differ 

 among different kinds of animals. Evidences of this 



