258 Modern Microscopy 



knowledge gained will be great, and will save many anxious 

 hours subsequently. Acquaintance with the condition of 

 the knife-edge necessary for good cutting is one of the 

 foundations of successful microtomy, and can only be 

 gained by practical work. 



Infiltrating: with Parafifin. — For the purpose of infiltra- 

 ting the object with parafSn wax many kinds of apparatus 

 have been devised ; a favourite in many quarters is the 

 Naples embedding bath, also several patterns made by the 

 Scientific Instrument Company of Cambridge enjoy con- 

 siderable reputation. All such apparatus are essentially 

 water-baths, modified in form to suit the necessities or ideas 

 of their various originators. One of the best, most useful, 

 and most simple infiltrating devices is the ordinary double- 

 walled, copper-drying oven of the chemical laboratory, the 

 space between the walls being filled with water, and kept at 

 a constant temperature by means of a gas-jet and mercury 

 regulator with a gas-pressure regulator. The very best 

 apparatus for this purpose is the ' Hearson ' vacuum oven. 



We might here mention that makeshift apparatus 

 should be avoided if one wishes to properly infiltrate 

 tissues. No good sections can ever be hoped for from tissues 

 in paraf&n wax that are not thoroughly infiltrated in every 

 cell, to the exclusion of all air and clearing agent. Never- 

 theless, for merely embedding in paraffin, a makeshift 

 apparatus might possibly answer. 



Infiltrating Oven. — The practical worker will find the 

 oven herein recommended to fulfil his requirements in a 

 very perfect manner, both for infiltrating and for the many 

 purposes for which a hot chamber is requisite. The great 

 advantage of the plain copper water-oven over its em- 

 bedding-bath competitors is that the door can be closed, 

 and dust, damp vapours, and all other annoyances kept 

 outside. It is also available for its original purpose in the 

 chemical laboratory. Pig. 72 illustrates the apparatus used 

 by the writer in its working order ; the door is opened in 

 order to show the shelves inside. A description of this 



