212 The Microscope. 



the proportions. Cocoa butter and vaseline cannot be recommended 

 as a paraffin softener. 5. The formula for ammonia-carmine is : Take 

 one part, by weight, of the best "No. 40 " carmine, dissolve in 100 parts 

 of distilled water, and then add one part of aqua ammonise. Ex- 

 pose the fluid in a shallow dish, and protected from the entrance of 

 dirt, till the odor of ammonia is no longer or hardly perceptible. 



SECTION-CUTTING AND STAINING. 



In this lesson the art of making free-hand sections will be dis- 

 cussed, though at the present day microtomes or section-making 

 machines are so perfected and sold at a price within the reach of 

 nearly eveiy worker in microscopy, that the art is fast becoming ob- 

 solete. They, however, who have only worked with an improved 

 microtome would be surprised to see the perfection attained by an 

 experienced free-hand cutter. The wi'iter has in his possession a col- 

 lection of specimens cut in this primitive way some years ago in a 

 German laboratory; and though at the time no expert, he does not 

 consider them so very crude when placed by the side of work done- 

 at a later day, and with the most helpful appliances. They who 

 can afford it should, by all means, own a microtome, though such an 

 instrument is not absolutely essential to the performance of good 

 work. 



Imbedding. — In order that the specimen to be cut be evenly com- 

 pressed and, at the same time, firmly held, it is imbedded in some 

 substance which is itself easily cut. Paraffin is generally used for 

 this purpose. If the specimen be of delicate character or filled 

 with cavities it should, before imbedding, be thoroughly permeated 

 with the paraffin. To do this, place it — after hardening in alcohol 

 — in a large volume of chloroform and leave for twenty-four 

 hours. Now melt the paraffin-mass over the water-bath, and im- 

 merse the specimen in it, where it should remain for two hours, 

 when, on removing and cooling, it will be found quite firm. Care 

 should be taken that the paraffin be kept only at the melting point, 

 for if it be allowed to boil the specimen will be ruined. Objects 

 of firm texture such as liver, kidney, etc., do not need this pre- 

 liminary treatment. 



Of thin cardboard make a box about two inches in length and 

 one inch in width and depth. A pill -box of similar dimensions or a 

 Swedish match-box will also answer admirably. After melting the 

 paraffin-mass fill the pipette with it, and cover the box-bottom to a 

 depth of about three-eighth inch. Now take a piece of the hardened 



