The Celloidin Method 123 



and they are perfectly adapted to the requirements of photo- 

 micrography. The following is a brief abstract of Plowman's paper: 



1. Preparation of Material. Dead and dry material should be 

 repeatedly boiled in water and cooled to remove air. An air-pump 

 may be used in addition. Living material may be fixed in a mixture 

 of picric acid, mercuric chloride, and alcohol: 



Mercuric chloride, saturated solution, in 30 per cent alcohol . . 3 parts 

 Picric acid, saturated solution, in 30 per cent alcohol . . 1 part 



Fix 24 hours, and wash by passing through 40, 50, 60, 70, and 80 

 per cent alcohol, allowing each to act for 24 hours. 



2. Desifilication, etc. Silica and other mineral deposits are 

 removed by treating with a 10 per cent aqueous solution of com- 

 mercial hydrofluoric acid. The material is transferred to this solu- 

 tion from water or from the 80 per cent alcohol. The process may 

 require 3 or 4 days, with one or two changes of the acid and frequent 

 shaking of the bottle. An ordinary wide-mouthed bottle, coated 

 internally with hard paraffin, should be prepared, since the acid is 

 usually sold in bottles with narrow necks. The bottles are easily 

 prepared by filling them with hot paraffin and simply pouring the 

 paraffin out. Enough will stick to the bottle to protect the glass 

 from the acid. Wash in running w r ater 3 or 4 hours. 



3. Dehydration. Use 30, 50, 70, 90, and 100 per cent alcohol, 

 allowing 12 hours in each grade. 



4. Infiltration with Celloidin. There should be ten grades of 

 celloidin: 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 per cent. Transfer 

 from absolute alcohol to the 2 per cent celloidin. (We should prefer 

 a previous treatment with ether-alcohol.) The bottle should be 

 nearly filled, and the stopper should be clamped or wired in place. 

 Put the bottle on its side in a paraffin bath at 50 to 60 C. for 12 to 

 18 hours. Cool the bottle quickly in cold water, taking care that 

 the water does not get into the bottle. Pour out the 2 per cent 

 solution (which, as well as all the other solutions, may be used repeat- 

 edly), and replace it with the 4 per cent, and proceed in the same way 

 with the other grades. When the 20 per cent solution is reached, a 

 further thickening is gained by adding a few chips of dry celloidin 

 from time to time until the mixture is quite stiff and firm. Remove 



