DEHYDRATING AND EMBEDDING. 447 



ably arranged in this new quantity of paraffin. The paraffin cubes 

 or prisms prepared in this way are fused to a large block of paraffin 

 by means of a hot needle. This large block will be of such size 

 as lends itself to ready fixing in the object holder of the micro- 

 tome, and is high enough to enable suitable sections to be cut. 

 The microtome razor must be fairly parallel to a side of the 

 angular paraffin block in which the object is contained. If, how- 

 ever, as with such embedded preparations only quite exceptionally 

 happens, we cut, not with a cross but an obliquely-fixed razor, 

 then the paraffin containing the preparation should be cut in the 

 form of a three-sided prism, and care taken that the side next the 

 razor should be arranged parallel to it. 



The transfer from alcohol to paraffin through the intermediary 

 of chloroform has been proved best for our purposes ; but on the 

 other hand cedar oil has been specially recommended, and has the 

 advantage of great simplicity. For usual use w r e take not the 

 thickened oil needed for an immersion fluid for homogeneous 

 objectives, but the ordinary cedar oil often quoted in price lists as 

 ""for clearing". Some cedar oil is put into a small cylinder, and 

 absolute alcohol floated carefully upon it. The object is now 

 transferred from absolute alcohol into that which forms a layer 

 over the cedar oil, and slowly sinks through it into this latter. 

 The alcohol is then carefully poured or pipetted off again from 

 the cedar oil, and the object either transferred for half an hour 

 into half-and-half cedar oil and paraffin, and thence into pure 

 paraffin, or else laid at once in pure paraffin. Most objects 

 admit of this simplification in treatment, and even the transfer at 

 once into paraffin of the higher melting-point. In this they will 

 be already impregnated after about three hours, -and after cooling 

 will be ready to cut. 



Any double-walled warm chamber, such as is used as a dry- 

 ing chamber, or for culture experiments, can be used as a paraffin 

 oven. The space between the two walls is filled with water, into 

 which, or into the oven, a " thermo-regulator " or "thermostat" 

 projects, which regulates the passage of gas to the flame found 

 under the apparatus. Such ovens are made by many scientific 

 apparatus makers, and we figure a very suitable and comparatively. 

 inexpensive one made by A. Scholz, Breslau (Alte Taschenstrasse), 

 which, without thermo-regulator, thermometer or micro-burner, 

 costs 1 17s. This warm chamber (Fig. 157) has the advantage 

 that it consists of three sections admitting of different tempera- 



