THE Microscope. 149 
ply of oxygen therefore must be only that which can filter 
through all these barriers; with how little must it be satisfied ? 
And the food on which it grows so plump must also pass 
through the same way. The larve of some species are 
said to feed on the substance of the gall, but such is not 
the case here. The excrescence is intimately connected with 
the tree since, when the branch dies, the gall becomes 
a brittle, brown lump of dead matter inclined to be pu- 
verulent within. The circulation, even the very limited circu- 
lation of the winter, is essential to the life of the tumor and of 
the larvee, but that the latter absorbs nutriment from the sap 
although probable is only an inference. The whole subject 
needs investigating. It is a field into which some student ought 
to delve. 
—_—< ¢ >—_—__ 
STUDIES IN HISTOLOGY. 
Cc. H. STOWELL. 
LESSON IV. 
STAINING. 
le order to render the minute structure of tissues more clear 
and distinct it is usual to submit the cut sections to the 
action of some of the staining fluids. Some of the staining 
reagents will give a uniform color to the section while others 
will stain the different parts of a tissue unequally. Asa general 
tule it may be stated that slow staining in weak solutions gives 
better results than rapid staining in stronger solutions, yet it 
becomes necessary many times to use the stronger solutions, 
staining rapidly, and the results are generally satisfactory. 
There is a very long list of staining reagents and it is difficult to 
understand for what special purpose they were compounded. 
A very few solutions will answer for all general work and 
only a very few more for special work. There are three stain- 
ings that are good in every place and are therefore in constant 
use, haematoxylin, carmine, and picrocarmine. 
H#MATOXYLIN OR LOGWOOD STAINING. 
An aqueous solution is made as follows: 
Hematoxylin, dried extract, - - 60 grains. 
Acie Sp Ulysse f= 2" 2 = eS ae Pe Orerains. 
