NOTES AND MEMORANDA. 
83 
histology to colour tissues, both normal and pathological. Yet I do 
not find that anyone, until we did so, made use of these two reagents 
simultaneously, so as to obtain a composite colour different from 
that which each produced separately. Everyone knows, indeed, how 
soluble aniline blue is used as a matter of preference, and to save time, 
to colour elements and tissues which have been previously submitted 
to the hardening action of alcohol and chromic acid, although more 
time is required for those which have been submitted to the action of 
the latter reagent. 
It is also known that certain tissues, such as those of the spleen 
and the lymphatics, and the cerebral and spinal nervous tissues, retain 
their colour better and with more elegance when aniline blue is used ; 
that the preparations thus coloured do not lose the tint which they 
have acquired by the addition of the acids, whilst alkaline solutions 
and even glycerine affect them in time. A colouring matter possessed 
of such advantages is, however, but little employed compared with 
others, such as carmine, hematoxyline, &c. ; and I believe the reason 
to be that preparations coloured by means of aniline blue, although 
very elegant, do not show all their details so well differentiated and 
so plainly as can be done with other processes, for example, with 
picro-carminate. Blue staining, in general, but particularly that pro- 
duced by aniline blue, will not allow histological forms to be defined in 
all their details. I might almost say that the contours fail to be 
recognized, which prevents our distinguishing in a tissue rich in 
cellules the limits of the various elements. 
It is besides well known that picric acid (in a saturated solution) 
colours the morphological elements and not the amorphous substances 
(Robin). It follows from this that the tissues which have been sub- 
mitted to its action take a beautiful yellow sulphur tint, and do not in 
any way lose the distinctness of their outlines. This is owing to the 
fact that picric acid is a reagent which does not precipitate in a 
granular form the substances forming the tissues or elements on which 
it is made to act, whilst the contours of the nuclei, the nucleoli, the 
granulation, and the cell- walls do not disappear. Moreover, the action 
of picric acid is not like that of chromic acid, which enters into com- 
bination with the substances upon which it reacts (Ranvier) ; and it 
also constantly happens that coloured preparations, after being hardened 
by the latter acid, are completely deprived of their colour by repeated 
washings with water. The action of picric acid on tissues is therefore 
much less]detrimental than that of chromic acid. 
Whilst then the colouring properties of aniline and picric acid, 
when they act separately, are sufficiently well known, no one has until 
now (at least so far as I know) employed these two substances at the 
same time and on the same tissue, so as to obtain a different tint by 
their reciprocally modified action, and giving rise to some important 
peculiarities, especially in certain special tissues. 
The idea of using picric acid in combination with another sub- 
stance to obtain a third, unlike it, and whilst partly possessing the 
2)roperties of the component substances, also some other new pro- 
perties resulting from the mixture, is certainly not new, if wc refer 
