94 MICROSCOPICAL TECHNIQUE. 



ened by the carbon of the leaf; others were white, with pearl- 

 coloured nodules ranged along the rays of the^ stars, like so many 

 real pearls. 



Mr. Hopkins' method of preparing this object is as follows : — 

 A small piece of the dried leaf is placed upon a thin, flat copper 

 plate, and another flat copper plate is laid upon it to^.^keep it 

 straight. Strong pressure is not required. The plates are now 

 heated slowly over a flame until they become redjhot ; they are 

 then allowed to cool, and the upper plate is removed. The piece 

 of leaf is then found to be carbonised and considerably'shrunken. 

 Without replacing the upper copper plate, the lower plate with the 

 carbonised leaf is again brought to a red heat, and, lastly, the 

 flame is brought into actual contact with the leaf, thus removing 

 the last trace of carbon, having nothing but the stars and the 

 white ash. 



The object is very tender, but it may be handled with proper 

 care and may be mounted dry. If it is desired to secure the 

 stars separate from the ash, one or two incinerated leaves may be 

 placed in a small metallic box and shaken up until the leaf is dis- 

 integrated, when the stars may be picked out. — The Microscopical 

 Bulleti?i. 



Tissues Hardened in Formalin.— Dr. Mayer says* : — " The 

 preparation put on the market is used in a 3 — 5 per cent, solution, 

 as a fixative and hardening agent. The stronger solutions (10 per 

 cent, and more) harden better and more rapidly, but for a preserv- 

 ing fluid the lower concentrations are preferable. The advantage 

 of formalin is best shown in transparent tissues (cornea, cysts) ; 

 and wherever colours are to be preserved that would be destroyed 

 by Miiller's fluid or extracted by alcohol. The results with the 

 nervous system are very satisfactory, the relations of grey and 

 white matter remaining very distinct. One noteworthy feature is 

 that the vapours alone are excellent preservers, so that, if the spe- 

 cimen should happen to be incompletely immersed, it would 

 nevertheless keep very satisfactorily if it is kept from drying out. 

 Such an accident would prove fatal with most other methods. 

 For histological purposes the fixation is best obtained with more 

 concentrated solutions. 



* Journal of Insanity, July, 1895, p. 131. 



