120 Methods in Plant Histology 



dehydrated in absolute alcohol; treated with ether-alcohol; infil- 

 trated with celloidin; imbedded in celloidin; hardened in chloro- 

 form or alcohol; after which it is cut, stained, and mounted. 



Eycleshymer, who brought the celloidin method to a high degree 

 of efficiency, published in 1892 a short account, which may be sum- 

 marized as follows: Put the celloidin tablet, or fragments, into a 

 wide-mouthed bottle, and pour on enough ether-alcohol (equal parts 

 ether and absolute alcohol) to cover the celloidin. Occasionally 

 shake and add a little more ether-alcohol until the celloidin is all 

 dissolved. The process may require several days. The solution 

 should have the consistency of a very thick oil. Label this solution 

 No. 4. Solution No. 3 is made by mixing two parts of solution No. 4 

 with one part of ether-alcohol. Solution No. 2 is made by mixing 

 two parts of No. 3 with one part of ether-alcohol. Solution No. 1 

 consists of equal parts of ether and absolute alcohol. 



After dehydrating, the material is placed successively in solutions 

 1, 2, 3, and 4. For an object 2 mm. square, 24 hours in each solu- 

 tion is sufficient; for the brain of a cat, a week is not too long. 



A paper tray may be used for imbedding. Pour the object, with 

 the thick solution, into the tray and harden in chloroform for 24 

 hours; then cut away the paper and place the block in 70 per cent 

 alcohol for a few hours. The material may be left indefinitely in a 

 mixture of equal parts of 95 per cent alcohol and glycerin. 



Before cutting, the object is mounted upon a block of wood. A 

 block, suited to the microtome clamp, is dipped in ether-alcohol, 

 which removes the air and insures a firmer mounting. Dip the 

 block of wood in solution No. 3, and the piece of celloidin containing 

 the object in solution No. 1. Press the two firmly together, and place 

 in chloroform until the joint becomes hardened. 



Set the blade of the microtome knife as obliquely as possible. 

 Both the object and the knife should be kept flooded with 70 per 

 cent alcohol, and the sections, as they are cut, should be transferred 

 to 70 per cent alcohol. 



Stain in Delafield's haematoxylin for 5 to 30 minutes. Wash in 

 water for about 5 minutes, and then decolorize in acid alcohol (2 to 5 

 drops of hydrochloric acid to 100 c.c. of 70 per cent alcohol) until 



