1891.] MICROSCOPICAL JOURNAL. 39 



or paraffinc method, and is cemented to the sHde, that glycerine or 

 Farrant's medium may not be used, for, on the contrary, they may 

 often be employed with great advantage. 



Of the two, Farrant's medium is rather easier to handle, and gives 

 excellent results ; and it is a good plan in sections not serial, where, 

 of course, only one medium can be employed with advantage, to mount 

 sections in both it and balsam, for comparison. Advantages may be 

 so gained, not only from comparison, but in making out the structure 

 of the sections. 



n. Always fmish a mount with cement. 



With fluid mountants the need of a cement finish is obvious, but 

 with balsam mounts the necessities for its employment are not generally 

 recognized. One should always be used, however: first, because the 

 balsam will turn yellow if not protected, the yellowness gradually creep- 

 ing in under the cover-glass, from the edges which are exposed to the 

 air toward the centre; second, because the balsam will ultimately be- 

 come so hard that a slight jar will cause the cover-glass to fly ofl". 



These diflerent hints are submitted from personal experience, not 

 that they \v\\\ add anything to the knowledge of experienced workers, 

 but that they may point out to the less expert a few practical means 

 by which failure may be avoided or more satisfactory results obtained. 



Microscopy for Amateurs. 



Bv T. CHARTERS WHITE, 



(JIIBKETT CLUB. 



\^Continued from page i^.'\ 



Injection. — When the student has advanced so far in this course, he 

 may undertake the injection of the blood-vessels of such small mam- 

 malia as the rat or guinea-pig, with a view to the demonstration of 

 their circulating system. As this is an operation of some difficulty, re- 

 quiring much care, a knowledge of anatomy, even if it be but element- 

 ary in its character, will greatly assist. Injections of the circulating 

 system of such small animals are more easily done from the left side of 

 the heart ; and to reach this the directions generally given are to make 

 a longitudinal incision through the sternum or breast-bone, and stretch 

 the opening sufficiently wide to get to the heart. This way of com- 

 mencing is very embarrassing, and affords but small space for the deli- 

 cate manipulation required at the most critical part of the operation. 

 It is recommended because of fear of the injecting fluid escaping through 

 the intercostal arteries which run across the course of the ribs. But, in 

 a small animal, these are not of sufficient size to make any material 

 loss. They are not to be considered when the advantage of gaining 

 more loom is in view. Therefore it is better to make an incision 

 transversely across the thorax, about the distance of six ribs from the 

 clavicle or collar-bone. Then, with a stout pair of scissors, cut 

 through the ribs on each side, and remove the front of the thorax in one 

 piece. The lungs, then, apparently fill the whole cavity of the chest ; 

 but, on pressing them apart in the centre, the heart, in its pericardial 

 bag, will be found. The pcrlcardhtm may be opened and removed, 

 as may also the greater part of the lungs, unless it is desired to inject 



