
217 

On the Nature of the Silver Reaction in Ammal and Vegetable 
Tissues. 
By A. B. Macattum, M.A., M.B., Ph.D., Professor of Physiology in the 
University of Toronto. 
(Communicated by W. D. Halliburton, F.R.S. Received March 3,—Read 
April 6, 1905.) 
I. Introduction. 
Though the use of nitrate of silver as a reagent in histology has now 
a half century of history, and has been of the greatest service in elucidating 
the structure of some tissues, it has not yet been .determined how the reagent 
is affected by the tissues, or what compound or compounds in the tissues are 
responsible for the precipitate which becomes discoloured in the sunlight. 
‘There are, indeed, references to these points in the literature of the subject, 
but these are scanty, and they are not at all in accord, while the majority are 
only guesses or fanciful explanations of the reaction itself. It may even be 
said that the investigators who used the reagent directed the whole of 
their energies to determining what it showed trom the morphological side 
rather than what was involved in the reaction itself, and because of this 
there has been nearly 30 years of discussion on the question whether the 
results obtained with the reagent were trustworthy or were of the nature of 
artifacts. 
The principal value of the reagent to the earlier observers appeared to be 
the fact that, after impregnation with nitrate of silver, and exposure of the 
preparation to light, cell outlines were revealed, and thereby the structure of 
lymphatics and of lymph tissue were demonstrated, the outlines being shown 
through the brown reaction which they manifested in such preparations. 
Von Recklinghausen,* who was amongst the first to use the reagent for this 
purpose, held that the silver salt is deposited in what he regards as the 
cement substance between the cells, and that this cement material under the 
influence of ight reduces the silver. It was pointed that the reaction is not 
‘confined to the cell peripheries and intercellular material, for preparations 
‘sometimes showed the reaction present in the cytoplasm of the cells, but 
absent from the membranes and the intercellular structures. This condition 
was known as the positive reaction or positive image, and was attributed by 
Schweigger-Seidelf to the decomposition and redistribution of the silver 
* “Die Lymphgefisse und ihre Beziehung zum Bindegewebe,’ Berlin, 1862. 
+ “Ueber die Grundsubstanz und die Zellen der Hornhaut des Auges,” ‘ Berichte d. 
Kon. Sachs. Gesell. d. Wiss., Math.-Phys. Cl.,’ vol. 20, p. 305, 1868. 
VOL. LXXVL—B. Q 
