4 PREPARATION AND MOUNTING 



shall have been macerated in water, or some other agent, 

 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 is 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, i.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 cautioned 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 (i.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 usa 

 of the draw-tube is the true remedy for this. 



