870 SUMMARY OF CURRENT RESEARCHES RELATING TO 



such as precipitates, maceration, &c, Dr. Mayer recommends acid 

 alcohol — 



97 volumes 70 per cent, or 90 per cent, alcohol, 

 3 „ hydrochloric acid, 



for larger objects, particularly if they are designed for preservation 

 in museums. The fluid should be frequently shaken up, and the 

 object only allowed to remain until thoroughly saturated, then trans- 

 ferred to pure 70 per cent, or 90 per cent, alcohol, which should 

 be changed a few times in order to remove all traces of the acid. 

 For small and tender objects, acid alcohol, although preferable to 

 pure alcohol, gives less satisfactory results than picro-sulphuric acid. 

 Acid alcohol as above prepared loses its original qualities after 

 standing some time, as ether compounds are gradually formed at the 

 expense of the acid. 



5. Boiling Alcohol. — In some cases among the Arthropods, Dr. 

 Mayer has found it difficult to kill immediately by any of the ordinary 

 means, and for such cases recommends boiling absolute alcohol, which 

 kills instantly. For Tracheata this is often the only means by 

 which the dermal tissues can be well preserved, as cold alcohol pene- 

 trates too slowly. 



6. Osmic Acid. — Dr. Mayer employs osmic acid as a staining 

 medium for the hairs, bristles, &c, of the dermal skeleton of Arthro- 

 pods. The lustre of Sapphirina is preserved by this acid,* and 

 according to Emery, the colour of the red and the yellow fatty pig- 

 ments of fishes. Van Beneden found osmic acid the best preservative 

 fluid for the Dicyemidae, and Mr. Whitman's experience leads to the 

 same conclusion. - ]" 



Although Dr. Mayer seldom uses this medium where histological 

 details are required, he observes that in those classes of animals 

 whose bodies are easily penetrated with watery fluids, osmic acid is 

 seldom to be dispensed with. 



Bleaching. — It often happens that objects treated with osmic acid 

 continue to blacken, after removal from the acid, until they are 

 entirely worthless, and such results are even more annoying than the 

 difficulties in the way of staining. It has been said that the blacken- 

 ing process can be arrested by certain staining media, but it is certain 

 that picro-carmine will not always do this, as some of Mr. Whitman's 

 preparations of Dicyemidae show. It is therefore a very important 

 step which Dr. Mayer has taken in finding a method of restoring 

 such objects. The method J is as follows : — The objects are placed 

 in 70 per cent, or 90 per cent, alcohol, and crystals of potassic chlorate 

 (KC10 3 ) shaken into the liquid until the bottom of the vessel is 

 covered ; then a few drops of concentrated hydrochloric § acid are 



* See corrosive sublimate, p. 872. 



f One of the best objects for testing methods is found in Phronima sedentaria. 

 Here the cells and nuclei are so sharply defined that they can be seen in the 

 living animal, and so the effect of a preservative fluid can be easily studied. 



% A slightly modified form of the method originally given in Arch. f. Anat. 

 u. Physiol. (Du Bois Reymond and Reichert) 1874, p. 321. 



§ Nitric acid may be used instead of HC1. 



