103 The Microscope. 



in a water bath, and heat the water to 100"^ F. Shake the vessel 

 occasionally to facilitate the saturation of the tissue with the 

 chloroform, and in half an hour add very gradually (i. e., in small 

 pieces, one after the other) about 50 per cent, of paraffine. Keep 

 the lung in this mixture for one houi', and then transfer it to a bath 

 of pure paraffine kept for two hours at 3*^ F. above its melting^ 

 point. The tissue will then be thoroughly infiltrated with the par- 

 affine, and beautiful sections can be made without trouble with a 

 hand microtome and a sharp razor. The sections are passed through 

 three consecutive changes of warm temperature, and, finally, are 

 mounted in balsam and benzole. 



THE PREPARATION OF INSECT SPIRACLES. 



FR. DIENELT. 



I HE spiracles of insects furnish a wide field for the student, and 

 -*■ a great many instnictive and interesting mounts can be 

 secured with little trouble from the perfect insect, pupa or lava. In 

 most beetles the spiracles are found in the upper part of the 

 abdomen. Tiu-n the insect on its back and cut across the thorax 

 close to the abdomen ; turn again and insert a sharp knife into 

 the opening made, and cut around the whole abdomen. As soon as 

 there is room, insert a small stick of soft wood, sharpened to a flat 

 point, by means of Avhich the object can be held securely while 

 cutting. All the cutting should be done on the lower side, so that a 

 margin is left on the upper part, which can be trimmed easily, after 

 the object has become softened in liquor potasse. Steeping the 

 insect in this fluid for a couple of hours, will destroy all the viscera. 

 Now, holding the part down with the pointed stick, which for this 

 purpc)se is far superior to mounting needles, and with a camel-hair 

 pencil, remove the viscera and transfer the object to rain water, 

 renewing this two or three times to insure cleansing and to remove 

 the last ti'ace of potash. Keep on brushing till it is certain that the 

 object is clean, and then trim the edges to suit before a final 

 washing. If it is desired to mount the trachea hi situ, greater care 

 is necessary in treating, but they show very well through the skin. 

 Or, after most of the viscera have been removed, the tracheae can be 

 torn by a sawing motion with the back of the knife fi'om the spir- 

 acles and mounted separate. In mounting larv?e entire, they should 

 be left in the li(j[Uor potasse for a longer time. I have sometimes 

 left them in for a whole day without injury. In cleaning, it is 

 necessary to keep them in the position in which they are to be 

 mounted. Lan'ae of the Lepidoptera show best when mounted on 



