1877.] The Sledge Microtome. 207 
may be stowed away and investigated at any leisure moment. 
For example, during a few weeks at the seaside, material for a 
winter’s occupation may be very easily procured. Neither is there 
so much hurry in drawing, as when an animal is living we are 
afraid it may die. For the sake of controlling the observations 
made on the sections, sketches of the general structure may be 
made, thus enabling the student to remember where each partic- 
ular section must have come from. 
There, is however, one other consideration to be noted, namely, 
that every cut destroys a certain amount of tissue. Thus suppose 
that a worms as in Figure 27, be cut transversely, 
a good deal will be destroyed ; but if longitudinal 
sections be made of another specimen, then one will 
see parts that the cut destroyed before, and only 
those spots where the two sets of cuts would have 
crossed had they been on the same animal will be 
wanting in both series. But even if you merely , 
make a second series of cuts they will not destroy t 
exactly the same place as in the first series. t 
When only a few preparations of some tissue are wanted, this 
instrument permits a rapidity of work combined with a degree 
of nicety unattainable by any other means, and I do not hesitate 
to recommend it most highly both to those who are carrying on 
microscopical investigations and those who are forming amateur 
collections, for only a little care is requisite to enable even per- 
sons with unskillful or unpracticed hands to make preparations 
equal to the very best that have ever been produced. . 
To succeed in doing this, however, very great care must be 
‘paid to the way of preparing the object. The following method 
18 applicable in a great many cases, in all, in fact, except where 
there is any fat to be preserved, or where, as is not unfrequently 
the case in histology, a special method of hardening or staining 
has to be employed: If the object is some small animal it may be 
killed by putting it in an 0.1% osmic-acid solution or in picric 
acid, and then in alcohol for twenty-four hours or less, according 
to the size of the object, and finally in absolute alcohol in suffi- 
cient quantity to entirely remove all the water from the object. 
For this purpose thirty or forty times the volume of the object — 
18 necessary. If the object is a bit of tissue or some organ it — 
may be hardened in alcohol without any preliminary treatment. 
When the object is composed of loose tissue, and is not more 
than 3 m.m. in diameter, it may be colored in toto, thereby sav- 
