Beook : SuMMAEY OF Methods OF Microscopical Research. 163 



of lime, hydrochloric acid or nitric acid, in place of sulphuric acid, 

 has been used with good results. The mode of preparation is as 

 follows : — 



100 parts sat. sol. picric acid in water. 



8 „ hydrochloric acid containing 25 % H CI. 



or, in place of the 8 parts hydrochloric acid, 5 parts pure nitric acid 

 of 45 % N2 O5 may be used. These solutions act in most respects like 

 the picro-siilphuric acid, but the picric acid is not quite so easily 

 "withdrawn by alcohol. 



Alcohol. — In a certain antithesis to the working of picrosulphuric 

 acid stands that of alcohol. The latter causes in thick walled objects, 

 particularly in those which are chitinous, a more or less marked 

 maceration of the interior of the object, which presently begins to 

 decay. Again, strong alcohol fixes the salt of the externally adhering 

 sea-water on the walls of the object, and so hinders a proper penetra- 

 tion of the liquid. Afterwards when the object is required to be 

 stained, unless an aqueous solution of the staining medium is used, 

 by which the precipitated sea-salt would be again dissolved, a proper 

 staining of the interior cannot be obtained. In staining with 

 cochineal it appears that in consequence of the existence of sea-salt 

 crystals on the outside of the object, a grey green precipitate is 

 thrown down which often spreads over the whole object and makes it 

 unfit for use. This may, however, be avoided to a great extent by 

 first soaking the ol ject for a few hours in acid alcohol (1-10 parts 

 hydr(^chloric ai id to 100 parts of 70 % alochol). From what has 

 been said it will be seen that alcohol per se is not a desirable pre- 

 servative medium, at least for objects which are intended for 

 histological research. 



Acid Alcohol. — In order to avoid the maceration caused by ordinary 

 alcohol Dr. Mayer has tried a slight addition of Hydrochloric or 

 nitric acid to alcohol of 70 %, also to alcohol of 90 % with good 

 results. He finds the best proportion to be 3 of hydrochloric acid to 

 97 of 90 % alcohol. The object should only be allowed to remain in 

 the liquid until it has become thoroughly soaked through and then 

 transferred to pure 90 % alcohol. In order to ascertain how far the 

 process has gone, a little picric acid is dissolved in the liquid so that 

 on subsequent washing in clean alcohol the yellow colouring matter 

 shows how far the alcohol has penetrated. In the use of acid alcohol 



