144 IMBEDDING METHODS. 



impregnated (half to one hour), and which is then evaporated 

 at the melting point of the paraffin. Biitschli recommends a 

 paraffin solution melting at 35. (Such a solution is made of 

 about equal parts of chloroform and paraffin of 50 melting 

 point.) Or, in the case of larger objects, instead of evapo- 

 rating the chloroform (which is often a very long process, as 

 the chloroform must be completely driven off, or the mass will 

 remain too soft for cutting), Biitschli simply transfers them 

 from the bath of paraffin solution to a bath of pure paraffin. 



Giesbrecht's method (Zool. Anz., 1881, p. 484), more fully 

 stated, is as follows : 



Objects to be imbedded are saturated with absolute alcohol, 

 and then brought into chloroform (to which a little sulphuric 

 ether has been added if necessary, in order to prevent the 

 objects from floating). As soon as the objects are saturated 

 with the chloroform, the chloroform and objects are gradually 

 warmed up to the melting point of the paraffin employed, and 

 during the warming small pieces of paraffin are by degrees 

 added to the chloroform. So soon as it is seen that no more 

 bubbles are given off from the objects, the addition of paraf- 

 fin may cease, for that is a sign that the paraffin has entirely 

 displaced the chloroform in the objects. This displacement 

 having been a gradual one, the risk of shrinkage of the tissues 

 is reduced to a minimum. 



270. Stoves and Water-Baths. It is important that the paraffin 

 should not be exposed to a moist atmosphere whilst it is in the liquid state. 

 If a water-bath be used for keeping it at the required temperature, provision 

 should be made for protecting the paraffin from the steam of the heated 

 water. 



A very convenient apparatus for this purpose is that of Paul Mayer, which 

 will be found described at p. 146 of Journ. Roy. Mic. Soc., 1883. It may 

 be procured from the Zoological Station at Naples (address " Direzione dclla 

 Stazione Zoologica, Napoli "), or from M. Paul Rousseau, 17, Hue Soiilllot. 

 Paris. See also Amer. Natural., 1886, p. 910 ; and Journ. Roy. Mic. Soc., 

 1887, p. 167. 



Other similar forms of paraffin-heating apparatus are described in several 

 places in the same journal, as also in Zeit.f. wiss. JlliL-. 



But whenever the worker has gas at his disposition, it will be found 

 infinitely preferable to employ a regulating stove or thermostat. I recoin- 

 iiu-iid the form described in POL'S Lehrbuch, p. 121. Other descriptions of 

 similar apparatus will be found also in the above-named journals. 



271. Imbedding IN VACUO. There are objects which, on account of their 

 consistency or their size, cannot be pcin-t rated by paratlin in the ordinary 



