IMBEDDING METHODS (PAEAFFIN). 101 



Other similar forms of paraffin heating apparatus are described in several 

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



Amongst apparatus arranged for heating by means of petroleum or similar 

 combustibles other than gas may be mentioned the stove manufactured and 

 sold by F. SANTORIUS, Gottingen (Zeit. f. iviss. MiJc., x, 2, 1893, p. 161), 

 and that of ALTMAXX (ibid., p. 221, cf. Centralb. f. BaJcteriol., xii, 1892, 

 p. 654); also that of KAEAWAIEW, Zeit.f. iviss. Mile., xiii, 2, 1896, p. 172. 



For ordinary work it is by no means necessary, though it may be con- 

 venient, to possess one of these costly and complicated heat-regulating con- 

 trivances ; a spirit lamp with the wick well turned down, or a night-light, 

 will suffice to keep the temperature constant enough, if watched occasionally. 



Ovens are, I think, only necessary in laboratories where several students 

 have to work with the same apparatus; for the private worker I think the 

 water-bath is more convenient. 



131. Imbedding ix 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 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 pre- 

 venting 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 vacua. 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 HOFFMAXN 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. This arrangement 

 is very efficacious and very simple if the laboratory possesses a supply of 

 water under sufficient pressure. 



In order to obtain the requisite vacuum without the aid of water under 

 pressure, a simple little apparatus has been designed by FBAXCOTTE (Bull. 

 Soc. Bdg. Mic., 1884, p. 45). In this the vacuum is produced by the con- 

 densation of steam. 



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

 simplifies the arrangement for containing the paraffin. The paraffin is con- 

 tained 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 to make sure that no more bubbles rise, then let the air in, 

 turn out the object with the paraffin (which by this time will have become 

 abnormally hard), and re-imbed in fresh paraffin. 



See also a paper by PIUXGLE, in Journ. Path, and Bacterial., 1892, p. 117 ; 

 or Journ. Roy. Mic. Soc., 1892, p. 893. 



