OP THE MICKOSCOPE. 195 



allowing plenty of time for the alcohol to displace the water, 

 and for the turpentine to displace the alcohol; and manipula- 

 ting the insect with great care, so as not to break any of the parts. 

 The eyes of insects are prepared by macerating them in very weak 

 potash, and, while still soft, pressing them between two slips of 

 glass. If allowed to harden before being pressed they will 

 split at the edges. The handsomest preparations of eyes are 

 obtained by taking a thin slice from a large eye, such as that 

 of a 'dragon fly, and treating it as directed. 



The feet of insects are in general easily prepared. Moderate 

 soaking in potash, careful washing in water, thorough soaking 

 in alcohol and turpentine, and careful management in properly 

 displaying them on the slide, are the secrets of success. The 

 student who wishes to make a careful study of these objects, 

 however, should place them in glycerine, after soaking them in 

 potash and thoroughly washing them. They should of course 

 be deposited in a cell filled with liquid, and then covered with 

 thin glass, and examined. The so-called tongues, etc., of in- 

 sects require no potash, being sufficiently transparent without 

 it, and after being soaked successively in alcohol and turpen- 

 tine, they may be mounted in balsam. When wanted for exam- 

 ination merely, immerse them in dilute glycerine, and if the 

 student can succeed in mounting them in cells, in glycerine or 

 some of the gelatinous media hereafter described, they will show 

 their structure to far better advantage than in balsam. 



In determining the character of what is brought into view by 

 the processes detailed, great aid will be derived from the use 

 of chemical tests. Thus, in the case of the potato, previously 

 described, most persons who had read anything at all upon such 

 sub j ects, would recognize the starch granules. All starch granules, 

 however, are not of the same form as those found in the potato; 

 indeed, some would hardly be recognized at all, except by those 

 having considerable experience. But if a little of the tincture 

 of iodine be brought into contact with them, they at once be- 

 come deeply blue. This subject is too extensive to be dis- 

 cussed here, but those who desire to become proficient in the 

 use of the microscope cannot safely neglect it. 



In most cases after an object has been carefully brought into 

 proper mechanical condition, in one of the ways we have de- 



