BULLETIN 39, UNITED STATES NATIONAL MUSEUM. [44] 



four hours, until all the acid is removed. This washing is easily accom- 

 plished by i)utting- the organisms in a jar with a wide mouth, over 

 which a piece of coarse, cheap muslin or cheese cloth is tied ; a small 

 hole in the cloth may serve to permit passing a rubber hose, from any 

 convenient water tap, into the jar, through which a gentle and con- 

 stant flow of water may be thus maintained. 



The addition of from one to one and one-half parts of acetic acid to 

 every one hundred parts of the chromic-acid solution improves the result 

 for histological purposes in cases where there are no calcareous parts 

 to be injured and acted upon by the acids. 



A very cheap and very excellent reagent for fixing and hardening" 

 the tissues of large mollusks is Miiller's fluid. This may be made up 

 as follows for gallon lots of the fluid : To every gallon of water take 3 

 ounces of j)ulverized bichromate of potash and 1 J ounces of sulphate of 

 soda (Glauber's salts). These salts may, in fact, be i^owdered together 

 in the quantities stated per gallon and put up in packages, each of 

 which would thus contain 4| ounces of the powdered and mixed salts, 

 sufficient to make 1 gallon of the mixture. The salts should be com- 

 pletely dissolved in the water before using. 



The action of this last reagent is slow and requires some attention,, 

 as do all of the processes given. Several volumes of the fluid should 

 be used to a single volume of organisms or tissues. The hardening 

 should be done in a cool, dark place. The fluid should be changed the 

 first two or three days every day, then every other day, then twice a 

 week, then once a week, till at the end of three to six weeks the harden- 

 ing is completed, larger objects taking the longer time. It is also 

 desirable to let the hardening go on in a dark closet or cupboard. 



After the hardening in Miiller's fluid the objects should be well washed 

 with water, as recommended for chromic acid, under a tap in ajar cov- 

 ered with cheese cloth for twenty-four hours or more, according to th& 

 size of the objects. Objects hardened and fixed in Miiller's fluid are 

 almostor quite as good for the i)urposeof studying surface details as those 

 hardened in chromic acid, and are as good for purposes of dissection as^ 

 objects carefully hardened in alcohol. 



After washing the objects hardened in Miiller's fluid they should be 

 placed in 70 per cent alcohol for permanent preservation. The 70 per 

 cent alcohol is readily made with a sufficient approximation to accuracy 

 by remembering that by adding nearly four- tenths of its volume of water 

 to the ordinary 95 to 97 per cent alcohol of commerce an alcohol i3er- 

 centage of 70 is reached. Thus with an ordinary foot-rule the operator 

 can mix his alcohols in cylindrical jars, thus: 



Stand the jar upon the table, place the rule by the side of it with 

 the scale next the glass, then pour in alcohol till some arbitrarily chosen 

 tenth division of the rule outside is reached by the surface of the spirit, 

 then add water to the spirit to the amount of nearly four more similar 

 divisions of the rule, when the requisite dilution of 70 per cent approxi- 



