APPENDIX. MICRO-REAGENTS. 



207 



of the eye piece. In the middle of the silvered surface of the prism is a small 

 aperture, smaller than the pupil of the eye, through which the microscopic 

 image is seen directly at the same time that the pencil and paper are perceived 

 by the double reflection. This camera has the advantage that it is used with 

 the microscope in the upright position. 



The following pieces of apparatus, though useful, are not really indispens- 

 able for such a course as here laid down : 



A microtome, for cutting sections accurately and uniformly of a given thick- 

 ness. A complicated and expensive form is not desirable. 



A turn-table as an aid in mounting objects. 



A good magnifying glass of about one inch focus, so mounted that it may 

 be adjusted to focus, and that both hands may be left free for manipulating the 

 object. The low power objective will serve the purpose of such a lens, and the 



Fig. 462. — Camera Lucida. 



student may readily devise for himself a stand for it which will serve the pur- 

 pose. Such an instrument is useful in preparing tissues for examination with 

 the compound microscope, for making dissections in the preliminary study of 

 certain structures, etc. 



MICRO REAGENTS. 



Iodine Solution. One of the most generally useful iodine preparations is 

 the following : 



Saturate a small quantity of distilled water with iodide of potassium, then 

 dissolve in it all the metallic iodine the solution will take up, and afterward 

 dilute the solution until it has a rich sherry color. It stains starch blue and 

 protoplasm a yellowish-brown. It also stains lignified tissue a brownish color. 

 As a test for starch grains in cells, the solution should be used quite dilute, 

 otherwise the grains will be so deeply colored as to appear black. Along with 

 sulphuric acid it may also be used as a test for cellulose tissues as follows : 

 Treat the section first with the iodine solution for a few minutes, and then with 

 a mixture of two volumes of strong sulphuric acid to one of water. The cellu- 

 lose tissues will slowly acquire a purple color, while lignified tissues will be 

 stained brown. 



