326 



SrMMARY OF CUERKNT RESEARCHES, 



out in the usual way, then dissected out together with as little of the 

 surrounding tissue as possible, an operation performed with the aid of 

 an ordinary dissecting microscope. It may be advisable to look at 

 the group of chromosomes from both sides. To do this, the metal 

 holder, instead of having a three-quarter inch perforation, should have 

 a much smaller perforation, say about one-eighth of an inch. Instead 

 of using a 8 by 1 in. glass slide, cement to the inside of the metal 

 holder a thin cover-glass several sizes larger than that to be placed 



Fig. 6. — A metal holder for clamping a microscopic object between 

 two thin cover-glasses, a, metal holder; h, steel spring as illus- 

 trated in figs. 4 and 5 ; c, small round cover-glass ; d, rectangular 

 cover-glass imderneath the round cover-glass ; e, notches in the 

 metal holder for the reception of the spring. This holder enables 

 the microscopist to look at the object vfith an immersion lens from 

 either direction. 



over the object. As the metal holder, in order to be stiff enough, has 

 to be several times thicker than the bowed spring, it may be advisable 

 to bevel the edge of the round aperture in the holder, so that it will 

 interfere as little as possible with the use of an immersion objective. 

 On a slide constructed in this manner, the object is held between two 

 cover-glasses,^ and hence may be viewed from either side with equal 

 ease. Such a slide furthermore permits the use of an immersion lens 

 as a condenser, a proceeding that has advantages. 



