174 



Mr. A. N. Drury. The Validity of the 



Summary. 



Experiments were made which prove that the results obtained by Unna with 

 rongalit white do not justify his assumption that it is a specific stain for the 

 oxygen place in tissues ; consequently his theory of staining by oxidation and 

 reduction is not proven. Further experiments were performed to find the 

 effect of the gases condensed on to a surface upon the depth of staining. 



Altering a surface by preliminary treatment with various chemical 

 substances also has a marked effect upon the subsequent condensation of 

 methylene blue. 



I should like to express my thanks to Mr. Hardy for help and criticism. 

 The expenses of this research were defrayed by a grant from the Thruston 

 Memorial Fund, Gonville and Caius College, Cambridge. 



[Note by W. B. Hardy. — The fundamental uncertainty in all microchemical 

 tests, and perhaps especially in those for oxidation places, may be put as 

 follows : — It is easy, as the writer found many years ago, to get discrimi- 

 nating colour reactions in sections and unfixed cells with oxidisable bodies 

 such as Wiirster's tetra-substance, which is a singularly delicate test for 

 what is called active oxygen — that is to say, for oxygen whose chemical 

 potential is raised above that of atmospheric oxygen by, e.g., ionisation or 

 the formation of peroxide. When oxidised it becomes a vivid purple and 

 the purple reaction is given very definitely by, e.g., the basophile granules 

 of leucocytes when the cells are exposed to a trace of the substance. But 

 the tetra-substance is itself unfortunately a basic substance and would 

 therefore be condensed from solution by the basophile granule in the 

 ordinary process of staining. 



There appear to be three possibilities, and experiment seems unable to 

 choose between them : — 



1. That the basophile granule is in fact a region where active oxygen 

 is produced, e.g., in the course of some local oxidation process. 



2. That the tetra-substance is oxidised indiscriminately about the section 

 during manipulation, in the course of which it is probably exposed to the 

 combined influence of evaporation and light ; * and that it is subsequently 

 condensed on to the basophile granules by a simple staining process. 



3. That in the process of condensation of an oxidisable body by surface 

 energy its chemical potential is raised, so that oxidation, which would not 

 otherwise occur in the presence of atmospheric oxygen, actually does occur. 

 It must be noted that the condensation is due solely to surface forces, 



* D'Arcy and Hardy, 'Journal of Physiology,' vol. 17, p. 390 (1894). 



