22 NUCLEAR STAINS. 



are not permanent. These objections certainly do not apply 

 to Ehrlich's solution, a -quantity of which, made five years 

 ago, is now in perfect order, and sections are still good which 

 were stained and mounted four and five years since. 



In order to change the violet colour of the sections into 

 blue it is usual to soak them for some hours in "tap water," 

 on the supposition that the alkalinity of the Carbonate of 

 Lime, dissolved in most natural waters, was necessary to the 

 change. That this is not the case is evident from the fact that 

 sections stained in a well-matured Ehrlich's Hsematoxylin 

 solution (which of course is itself acid) will become blue in 

 pure Distilled Water, freed from even the slightest trace of 

 Ammonia. The change, however, is undoubtedly assisted by 

 a trace of Alkali, and when sufficient Lime Carbonate does 

 not exist in the water, uniformly good results can always be 

 obtained in a few minutes by using Distilled Water con- 

 taining 1O grains of Bicarbonate of Sodium to the 

 pint (20 ounces). Light is in no way essential to the 

 development of the blue colour, and direct sunlight should 

 be carefully avoided on account of its bleaching action. 



After the blue colour is developed, transfer the sections to 

 70 p. c. Alcohol, as the colour fades much more quickly when 

 kept in water. 



It is occasionally stated that previous to staining the 

 sections must be freed from every trace of acid, as otherwise 

 the colour will not be permanent. Considering that one of 

 the best stains is itself acid, and that Acidulated Water or 

 Alcohol may freely be used to remedy overstaining, it is much 

 more to the point that sections, after the staining process is 

 completed, should be carefully freed and preserved from any 

 trace of acidity, more particularly when using counter- stains. 

 Freshly prepared solutions of Haematoxylin stain badly and 

 diffusely. When exposed to the air in strong daylight they 



