FIXING AND STAINING METHODS. 249 



well-washed preparations are now laid in watch-glasses with P. 

 Mayer's alum-carmine, or P. Mayer's para-carmine. The material 

 should lie in the carmine stain for several hours. Another portion 

 of the threads can be stained in P. Mayer's alum-haematin. It 

 is best from time to time to control the depth of the staining by 

 slight examination under the microscope, and to take the material 

 out when it has stained sufficiently. This is perhaps best effected 

 if, instead of staining in a watch-glass, the process is carried on 

 upon an object-slide, in which a round or oval hollow has been 

 ground. The slide can be placed bodily on the stage of the 

 microscope, and is handier in use for this than a watch-glass. If 

 in spite of this care the object should be overstained, that is, has 

 been stained too deeply, it should be laid in pure water, or in 

 about 1 per cent, watery alum solution, and left in till the depth 

 of the stain has been reduced so far as needed. In order to be able 

 to stain a picric preparation according to the ammonia-haeinatin 

 method, we must have previously removed from it every trace of 

 picric acid. For this purpose we transfer it to a comparatively 

 large quantity of boiled water, which we repeatedly change. In 

 this water, freed from carbonic acid gas by its previous boiling, the 

 object remains for twenty-four hours, after which it can be stained. 

 For this purpose we put some crystals of hsematoxylin in a small 

 quantity of distilled water, and aerate it with ammonia gas. This 

 latter we effect with the aid of a wash- bottle containing some 

 ammonia solution, in which the two glass tubes do not reach the 

 fluid. The haematoxylin crystals now dissolve- with a beautiful 

 violet colour. The solution is greatly diluted with distilled water, 

 and the preparation allowed to lie in it for some hours. The exact 

 time for coloration can here also be directly controlled. The pre- 

 paration is, with advantage, somewhat overstained, and afterwards 

 steeped for several hours in distilled water. This method of stain- 

 ing is somewhat troublesome, but often gives, however, the most 

 exquisite results. Preparations hardened otherwise than with 

 picric acid are little suited for staining with amrnonia-hseinatin. 

 The preparations treated with alum-carmine are also washed with 

 distilled water. If the protoplasm remains somewhat stained, the 

 stain can be removed by 1 per cent, alum solution or J to 1 per 

 cent, solution of hydrochloric acid. If the staining has been 

 with para-carmine the washing can be with a suitably weak solu- 

 tion of aluminium chloride in alcohol, and, if this does not suffice, 

 with alcohol containing 5 per cent, of acetic acid. 



