24 CUTTING A^D MOUNT! \(i Tlssi'KS. 



In the case of delicate tissues, like fern prothallia, or the 

 apical cell of Nitella or Chara, some little variation is made from 

 the regular method and a detailed description of the process may 

 be of value. (The Microscope, Nov. 1893.) 



The material is first placed in 10 per cent, alcohol in a dehy- 

 drating apparatus and allowed to remain for 24 hours, when it is 

 taken out and placed for one hour in 95 per cent, alcohol to insure 

 complete dehydration. After this the tissue is placed in a 1 per 

 cent, solution of collodion and allowed to remain in a tightly corked 

 vial for 12 hours. The cork is then removed, and by slow evapora- 

 tion of the ether and alcohol, the collodion will thicken. When it 

 is of the consistency of ordinary glue, the preparation is poured 

 out of the vial, with the collodion, into a paper boat, of the kind 

 used in paraffiue imbedding, or an ordinary watch glass will answer 

 the purpose. The thick collodion is then poured over the tissue 

 and allowed to harden in the air until a firm film has formed over 

 the surface. After this the mass is placed in a jar of 85 per cent, 

 alcohol and allowed to remain from 5-6 hours until the collodion is 

 quite tough. Then with a thin knife cut out a block of collodion 

 containing the tissue inside. The block can be placed in any 

 desired position on the end of a cork and held while thick collodion 

 is poured over, until it is covered. Each coat as added should be 

 allowed to slightly harden before applying the next, until the 

 operation is completed. After the whole has become firm in the 

 air, it is placed in a jar of 85 per cent, alcohol where it should 

 remain 6 to 8 hours. The operation of sectioning and mounting is 

 the same as outlined for the firmer tissues. 



In order that the sections may be all arranged the same side 

 up, the block of collodion, which should always be trimmed at the 

 top, can be cut with a notch near one corner, and the notches all 

 arranged with the same relative position on the slide. 



It will be found that with this method perfect serial sections 

 of any desired thickness can- be obtained from objects which are 

 not more than one layer of cells thick, and thus render the prepara- 

 tion of delicate tissues but little more difficult than that of the 

 firmer kinds found in ordinary stems and roots. 



Many substances for infiltrating have from time to time been 

 suggested, and have met with varying success. The more irnpor- 



