176 Minot: Notes on Histological Techiiique. in, 2. 



It is possible to mount tlie preparations at once in fluid baisam, but I 

 find it more couvenient on account of the greater certainty of escaping 

 air bubbles, to clear up the shellaced specimeu with oil of cloves; 

 (other essential oils may be iised as well). The oil may be rcmoved iu 

 the ordinary mauner, by cigarrette paper, all the more readily because 

 the preparatiou will stand pretty rough handling. The oil of cloves 

 ought not to be left on the slide for more than half an hoiir as it 

 gradiially softens the shellac. 



The shellac iised should be that knowu as „refined," which gives 

 a perfectly clear Solution. It may be purchased of dealers in astists, 

 materials. The sections should be thoroughly covered and the thicker 

 they are the more shellac is required, If snfficient shellac is used the 

 finest histological details are preserved, so far as I have been able to 

 observe, unaltered during the drying process. Without euough shellac 

 ruinous shrinkage ocurrs. If the sections were imperfectly dehydrated 

 there appear opaque whitish spots in them after the drying. In this 

 case wash the slide over with 96% alcohol until the opaque spots have 

 disappeared ; drain off the alcohol by tiltiug the slide ; add a little 

 fresh shellac aud dry agaiu ; if necessary repeat the process imtil the 

 dried specimen has no trace of cloudiness. 



This shellac method has other applicatious, It can of course be 

 applied to ordinary sections frora which the imbedding substance has 

 been removed. It is however particularly serviceable for mounting teased 

 preparations, isolated cells, and small organisms; these may be trans- 

 ferred frora alcohol to shellac, and after they have been arranged in 

 the latter on the slide in such positions as may be desired, the prepar- 

 ation is dried, and the mounting may then be accomplished without 

 the fragments moving frora their place. 



5. Method s ofhardening. The use of warmth with MtJLLER's 

 fluid I find inferior to the use of cold. It seems to me that the best 

 result is obtained with slow hardeniug at a temperature but little above 

 freeziug. — It may perhaps not be undesirable to renew attention to 

 Fül's formula for picro-sulphuric acid, which is much preferable to the 

 older method hithei'to in vogue. — A word may be added in favour of 

 nitric acid, which in cases where the specimen is of small size, and 

 especially when from the deterioratiou having begun in it, it is desirable 

 to preserve quickly, is very valuable. We use now, one part of the 

 commercial concentrated acid diluted with nine parts water, the specimen 

 is placed in the acid for 3 to 5 minutes, then in runuing water for 

 15 to 20 minutes; in 30% alcohol 10 minutes; 50%, one hour; and 



