4 ON THE DIFFERENTIAL REACTION TO VITAL DYES EXHIBITED BY 



become so, would not appear to justify a withdrawal of attention from the fact that 

 the connective tissue is typically composed of but two cell strains — the phagocytic 

 and the fiber-forming elements, that no other elements can be said to constitute 

 its invariable make-up, and that these elements are at an early time sharply differen- 

 tiated and continue to be so throughout life. A long line of investigations by 

 modern histopathologists has served us here, but particular clarity has come from 

 the histological researches carried out by A. A. Maximow. 



Recent studies with entirely new methods, for example, the beautiful cyto- 

 logical analyses of tissue cultures by M. R. and W. H. Lewis, and similar in vivo 

 studies on Amphibia bj r E. L. and E. R. Clark, all support this simple idea. The 

 application of coloring-matters to the living animal — the so-called intra vitam 

 staining — has furnished us with a unique method for the recognition not merely 

 of fine structural but also of physiological cell differences. Very striking results 

 have been obtained with them, especially as regards the connective-tissue cells, 

 in the case of animals which have been submitted to treatment with trypan blue 

 and with isamine blue. These dj'es affect in a sharply different manner the two 

 great cell groups of the connective tissue and enable one to segregate them, with 

 far greater precision than has hitherto been possible, into two definite cell classes'. 

 It is unnecessary for us to maintain, however, that this striking reaction can serve 

 as an utterly reliable criterion of cell species and of cell relationships or transforma- 

 tions. 'It is necessary only that we recognize in it a selective histo-pathological 

 reagent of great beauty which separates sharply the strains of connective-tissue 

 cells existing at any one time into two functional types without appreciable inter- 

 grades. From the standpoint of the physiological significance of cell differentia- 

 tion, this fact justifies all the scrutiny we can accord it, but especially as it involves 

 the whole question of the fundamental nature of the reaction between living proto- 

 plasm and these dyes. We have attempted, consequently, in the present memoir, 

 to describe with appropriate detail the biological peculiarities of the two connective- 

 tissue cell types as far as they may be disclosed by their differential behavior towards 

 such substances as are embraced in the numerous dyestuffs of the acid-azo class. 



It is a safe prediction that he who has practised the study of living cells will 

 not willingly revert to other methods, except for their admitted value as controls. 1 

 It is a curious commentary on the history of histological research that the micro- 

 tome has greatly discouraged methods of direct observation of the living or sur- 

 viving cell, methods which may now bring to their aid modern improvements in 

 optical equipment and the discovery of specific coloring methods with vital dyes. 

 He who has prosecuted with patience such studies upon the connective tissue has 

 forced upon him the conviction of its unique effectiveness in differentiating cell 

 types where the fixed picture leads to confusion. 



The prolonged study undertaken by one of us in conjunction with W. Schule- 

 mann has had for its aim a comparative knowledge of the effects obtained with the 



1 Perhaps the extreme to which devotion to the section method may lead one may best be exemplified by our citation 

 of Maximow (1916), who is willing to declare the accurate and painstaking observations of the Lewises as "of but little 

 importance," because their transparent cultures were not embedded and sectioned. 



