30 MICROSCOPICAL RESEARCH 



to the extent of half a cell-wall, the juncture of the cells first showing a 

 slight lignification, and having an affinity for a stain giving a lignin 

 reaction, while the central portion of the cell-wall is still unlignified and 

 takes up a stain having an affinity for cellulose ; each stain gradually 

 merging into the other and in each case showing the deepest in colour 

 at that particular part having the greatest affinity for it. 



The production of a correctly stained section does not consist so 

 much in putting the stain into the tissues, as in washing it out ; the 

 finest preparations being those that have been overstained rather than 

 otherwise and the colour stripped out again, or reduced to the required 

 tint by the use of acid-alcohol or by a prolonged soaking in alcohol. 

 When a nuclear preparation only is required, the reducing operation 

 must be continued until the colour is removed from all the tissues except 

 the nucleus. When it is desired to double stain a preparation composed 

 of two or more tissues, it must be placed first into the stain having an 

 affinity for the primary ground tissue, and treated exactly as if staining 

 only for one colour, and then placed in the second or counter-stain. 

 After staining with the second colour, the sections should be rinsed 

 quickly in two or three changes of alcohol, and immediately the first 

 colour stands out clearly the process must be stopped by transferring 

 the sections to the clearing oil. 



As a simple example of staining, let us take Grenacher s formula of 

 borax carmine, which is practically a permanent stain for developing 

 tissue. To remove this stain from tissue for which it has an affinity 

 requires the use of acidulated alcohol, or to be left for weeks in alcohol 

 free from acid, or placed direct from the alcohol into water when 

 diffusion currents would be set up and the carmine liberated. 



On the other hand Malachite green, which is a counter stain to 

 carmine, having an affinity for formed or lignified tissue, may be 



