178 IMBEDDING METHODS. 



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 oil 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. 



277. 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 della 

 Stazione Zoologica, Napoli "), or from M. Paul Rousseau, 17, Rue Soufflot, 

 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. Mik. 



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

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

 mend the form described in FOL'S Lehrbuch, p. 121. Other descriptions of 

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



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

 consistency or their size, cannot be penetrated by paraffin in the ordinary 

 way, even after hours or days in the bath. For such objects the method of 

 imbedding in a vacuum renders the greatest service. It not only ensures 

 complete penetration in a very short time a few minutes but it has the 

 further advantage of preventing any falling in of the tissues such as may 

 easily happen with objects possessing internal cavities if it be attempted to 

 imbed them in the ordinary way. 



The principle of this method is that the objects are put through the 

 paraffin-bath in vacuo. In practice this may be realised by means of any 

 arrangement that will allow of maintaining paraffin at the necessary tempe- 

 rature for keeping it fluid under a vacuum. 



The apparatus of HOFFMANN will be found described and figured at p. 230 

 of Zool. Anz., 1884. In this arrangement the vacuum is produced by 

 means of a pneumatic water aspiration pump, the vessel containing the 

 paraffin being placed in a desiccator heated by a water-bath and furnished 

 with a tube that brings it into communication with the suction apparatus. 



