134 



CYTOLOGICAL TECHNIQUE 



section 



mounting medium 



covers lip 



slide 



adhesive 

 attactiing section 

 to slide 



Fig. 7. Diagram of a finished microscopical slide in sectional view, 

 showing adhesive s and varnish. 



secondly, the oxidation by atmospheric oxygen of the Hnoleic and 

 other unsaturated fatty acids contained in the linseed oil. This 

 oxidation is helped by heating the oil with lead monoxide in the 

 preparation of the varnish. The hardening occupies some days 

 after the varnish has been applied. 



All finished microscopical preparations of organisms and their 

 parts, other than those of living cells still lying in the fluid that 

 bathed them in their natural environment, are to be regarded as 

 products of the reaction between the living tissues and the various 

 media in which they have successively been soaked. The reaction- 

 products, which are what we study under the microscope, are only 

 informative about organisms and their life-processes if some 

 knowledge is available about the reactions involved; and this 

 presupposes knowledge of the reagents. It has been the purpose 

 of this book to supply information about the reagents that are 

 used in some of the simplest processes of routine microtechnique, 

 and about their reactions with tissue-constituents. 



If an unknown tissue or cell be acted upon by an unknown re- 

 agent, no useful information can be obtained. Cytologists and 

 histologists should be as loath to use secret reagents as doctors 

 are to use secret medicines. Quite a lot of fancifully named embed- 



