4, PREPARATION AND MOUNTING 
shall have been macerated in water, or some other ageut, 
for so long a time as may be required to loosen or dissolve 
the connective tissue. It is of these agents that we shall 
presently have to speak in detail, greater or less according 
to their relative importance. Boiling or steaming may 
often be employed with advantage. It must not be too 
hastily concluded that, because there is nothing at first 
visible, there 7s therefore nothing to be seen. There are 
many important tissues which are apparently structureless, 
or homogeneous, which yet are possessed of such diverse 
elements as absolutely to require some process by which . 
they may be optically or visually differentiated, if one may 
use such a phrase, 7.e., discriminated from the neighbouring 
tissues or organs. It is thus that their proper uses and 
purposes in relation to the whole organism may be correctly 
indicated or inferred, their histological nature decided, and 
their physiological relations and connections established be- 
yond doubt. 
The student is also very emphatically oabbioned against 
the use of objectives of very wide angle, as well as of 
deep eye-pieces. In the former case, the relations of 
structures to each other can never be well made out, since 
it is impossible to get a focus of any depth (z.e., of all the 
structures involved), in one view, because the objects in one 
plane only can be clearly seen, the rest, either above or below, 
being more or less out of focus, and therefore hazy and 
indistinct. 'This objection applies far less to those of lesser 
angle, which are therefore the best for histological purposes. 
In the latter case, we have nearly the same defect to con- 
tend with, viz., that surface markings only, or mostly, can 
be seen clearly (not to speak of the loss of light). The use 
of the draw-tube is the true remedy for this. 
