96 The Unity of the Organism 



the preface written by himself alone what was made out by 

 the observations : "It has been conclusively 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.' 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., as will be seen in the context. The question of 

 inter-breeding has, for instance, seemed perfectly clear in 

 the case of Canidae and Mnridae, and no difficulty was ex- 

 perienced in forecasting similarities and dissimilarities of 

 habit in Sciurldoe, Murldae, Felidae, etc., not because hemo- 

 globin is per se the determining factor, but because, accord- 

 ing to this hypothesis it sei"\'es as an index (gross though 

 it be, witli our present knowledge) of those physico-chemical 

 properties which serve directly or indirectly to differ- 

 entiate genera, species, and individuals." ^^ This investiga- 

 tion was extended to the blood of more than one hundred 

 species of vertebrates and included representatives of all 

 the classes of the phylum, though many more mammals 

 than any of the other classes were studied. In several gen- 

 era, as Canis and Felis, a number of species and varieties 

 were included. 



The crystallographic method was used almost exclusively 

 in the investigation. Concerning the value of this method 

 for recognizing cliemical similarities and differences, the au- 

 thors, trusting partly to such authorities as Groth, rest on 

 the view that "Differences of chemical constitution are ac- 

 companied by differences of pliysical structure, and tlie 

 crystallographic test of the differences of chemical consti- 

 tution is recognized as the most delicate test of such dif- 

 ferences." ^^ In accordance with this the dictum, "Sub- 



