PARAFFIN METHOD 83 



161. Imbedding in Vacuo. There are objects which, on account of 

 their consistency or their size, cannot be penetrated by paraflin in the 

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

 the method of imbeddins; under a vacuum (strictly, under diminished 

 atmospheric pressure) 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. It is realised by means 

 of any arrangement that will allow of keeping paraflin melted under a 

 vacuum. 



That of Hoffmann is 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. 



Francotte {Bull. Soc. Belg. Mic., 1884, p. 45) produces the requisite 

 vacuum by the condensation of steam. 



FoL (Lehrb., p. 121) employs the vacuum apparatus of Hoffmann, but 

 simplifies the arrangement for containing the paraffin. The paraffin is 

 contained in a stout test-tube furnished with a rubber stopper traversed 

 by a tube that puts it into communication with the pump. The lower 

 end of the test-tube dips into a water-bath. You pump out the air once 

 or twice, wait a few minutes, then turn out the object with the paraffin 

 (which by this time will have become abnormally hard), and re-imbed in 

 fresh paraffin. 



See also Pringle, in Journ. Path, and Bacteriol., 1892, p. 117, or 

 Journ. Roy. Mic. Sac, 1892, p. 893 ; Kolster, in Zeit. iviss. Mik., xviii, 

 1901, p. 170 ; Berg, Zeit. wiss. Mik., xxvi, 1909, p. 209 ; Fuhrmann 

 ibid., xxi, 1904, p. 462 ; Kolmer and Woi.ff, ibid,, xix, 1902, p. 148 ; 

 Gemmill, Journ. Roy. Mic. Soc, 1911, p. 26. 



162. Imbedding and Orientation. As soon as the objects are 

 thoroughly saturated with paraffin they should be imbedded by 

 one of the niethods given above (§§ 155 et seq.) and the paraffin 

 cooled as described next §. 



But it may be desirable to have the object fixed in the cooled 

 paraffin in a precisely arranged position, and, above all, in a 

 precisely marked position. Very small objects may be oriented 

 as follows : — The object is removed from the melted paraffin, 

 and placed on a cylinder of solid paraffin. A needle or piece of 

 stout iron wire is now heated in the flame of a lamp, and with it 

 a hole is melted in the end of the cylinder ; the specimen is pushed 

 into the melted paraffin, and placed in any desired position. The 

 advantages of the method lie in the quickness and certainty with 

 which it can be performed. In using the needle it is important 

 to melt as little paraffin as possible at one time, in order that that 

 which is melted may cool again as rapidly as possible. 



Kerr {Quart. Journ. Micr. Sc., xlv, 1901, p. 4) employs an 

 electrically heated needle. 



For the exact orientation of fairly large objects, such as embryos, 

 it is helpful, in a darkened room, to apply a powerful beam of 

 light which passes without much obstruction through the paraffin 



