102 MICROSCOPICAL RESEARCH IN THE 



surface of marine animals, and thus a crust is formed which 

 prevents the penetration of the fluid to the interior.* 



(4) This crust also prevents the action of staining fluids, except 

 aqueous solutions, by which it would be dissolved. 



Notwithstanding these drawbacks, alcohol is still regarded at 

 the Naples Aquarium as an excellent fluid for killing many animals 

 designed for preservation in museums or for histological work. In 

 many cases the unsatisfactory results obtained are to be attributed 

 not to the alcohol per se, but to the method of using it. Most of 

 the foregoing objections do not, as Dr. Mayer has expressly 

 stated, apply to fresh-water animals ; and Dr. Eisig informs me 

 that he has no better method of kiUing marine annelids than with 

 alcohol. Judging from the preparations which were kindly shown 

 to me, and which were all beautifully stained with borax-carmi?te, 

 Dr. Eisig's mode of treatment must be pronounced very success- 

 ful. The process is extremely simple. A few drops of alcohol 

 are put into a vessel which contains the annelid in its native 

 element, the sea-water; this is repeated at short intervals until 

 death ensues. After the animal has been thus slowly killed, it 

 may be passed through the different grades of alcohol in the 

 ordinary way, or through other preservative fluids. Objects killed 

 in this manner show no trace of the external crust of precipitates 

 which arises where stronger grades of alcohol are first used. The 

 action of the alcohol is thus moderated, and the animal, dying 

 slowly, remains extended and in such a supple condition that it 

 can easily be placed in any desired position. The violent shock 

 given to animals when thrown aHve into alcohol of 40 per cent, to 

 60 per cent., giving rise to wrinkles, folds, and distortions of every 

 kind, is thus avoided, together with its bad effects. 



3. Acid Alcohol. — In order to avoid the bad effects of alco- 

 hol, such as precipitates, maceration, etc.. Dr. Mayer recommends 

 add alcohol — 



* Dr. Mayer first noticed ^his in objects stained with Kleinenberg's hasma- 

 toxylin, and afterwards in the use of cochineal, where a grey-green precipitate is 

 sometimes produced, which renders the preparation worthless. Such results may be 

 avoided by first soaking the objects a few hours in acid alcohol (i— 10 parts hydro- 

 chloric acid to 100 parts 70 per cent, alcohol). 



