106 THE MICROSCOPIST. 



and with a dry needle push the blood to the edge that it 

 may be just moistened with the glycerin. Place the slide 

 on the cover so that the glycerin edges of the cavity may 

 adhere, and turning it over, transfer it to the stage of the 

 microscope. Thus a minute quantity of a strong solution 

 of hsemoglobulin is obtained, the point of greatest density 

 of which may be found by a one-fourth objective, and 

 tested by the spectroscopic eye-piece and witlrhigh powers. 

 The tiny drop may be afterwards wiped off with moist 

 blotting-paper, and a little fresh tincture of guaiacum 

 added, showing the blue color of the guaiacum blood-test. 

 Inverted Microscope of Dr. Lawrence Smith. In ordinary 

 chemical investigations there is some risk of injuring the 

 polish of the lenses, as well as the brass work of the mi- 

 croscope, without very great care. This is particularly 

 the case in observing the effects of heat or of strong acids. 

 To obviate this difficulty, Dr. Lawrence Smith contrived 

 a plan for an inverted microscope, w r hich has been con- 

 structed by Cachet of Paris. The optical part of the in- 

 strument is below the stage, and is furnished with a pecu- 

 liar prism, by which the rays from the'objective are bent 

 into a conveniently inclined body. The illuminating ap- 

 paratus is above the stage. This, construction renders the 

 instrument well adapted to chemical investigations. 



GENERAL MICROCHEMICAL TESTS. 



Dr. Worm ley has directed attention to some necessary 

 cautions. He shows that many substances which may 

 readily be detected in a pure state, even in very minute 

 quantities by the microscope, are difficult to detect when 

 mixed \vith complex organic materials. This is especially 

 applicable to the alkaloids, which should be separated 

 from such mixtures by the use of the dialyzer a hoop 

 with a bottom of parchment-paper, etc. or extracted 

 with ether or chloroform. 



