38 MANUAL or BACTERIOLOGY. 



hyde, with 90 parts water make a good mixture for fixation; 

 after twenty-four hours change to alcohol. 



Imbedding in Collodion or Celloidin.— From alcohol the 

 pieces of tissue are placed in equal parts of alcohol and ether, 

 twenty-four hours; thin collodion (i| per cent.), twenty-four 

 hours; thick collodion of a syrupy consistency (6 per cent.)," 

 twenty-four hours. The specimen is laid upon a block of 

 wood or, better, the compressed vegetable fibre called vul- 

 canite, and surrounded by thick collodion, and then placed 

 in 70 per cent, alcohol. The collodion makes a firm mass, 

 surrounding and permeating the tissue, and permits very thin 

 sections to be cut. The soluble cotton sold by dealers in 

 photographers' supplies serves as well as the expensive prep- 

 aration known as celloidin. To make collodion, dissolve it 

 in equal parts of alcohol and ether. Soluble cotton is also 

 called pyroxylin, and is a kind of gun-cotton. 



Imbedding in Paraffin. — Pieces of tissue 2 to 3 mm. 

 thick which have already been fixed in alcohol or formalde- 

 hyde are to be placed : 



(a) In absolute alcohol for twenty-four hours. 



(b) In pure xylol one to three hours. 



(c) In a saturated solution of paraffin in xylol one to three 

 hours. 



(d) In melted paraffin having a melting-point of 50° C, 

 which requires the use of a water-bath or oven, one to three 

 hours. The xylol must be entirely driven off, and the tissue 

 thoroughly infiltrated. 



(e) In fresh parafSn for one hour. 



The tissue is finally placed in a small dish or paper box 

 and covered with the melted paraffin. The paraffin should 

 be hardened as quickly as possible with running water. It 

 is important to fix the piece of tissue in the desired position 

 before pouring in the melted paraffin. 



Paraffin imbedding is especially useful when serial sections 



