NhtlVOUS SYSTEM GENERAL METHODS. 383 



If the latter, add a little soap to prevent it from running into 

 drops on the knife. 



If the collodion method has been taken it may be found 

 that notwithstanding every precaution the collodion has not 

 thoroughly penetrated the tissues. Good sections may, how- 

 ever, still be obtained by DUVAL'S method of collodionising 

 the sections. The cut surface of the tissue is dried by 

 blowing on it, and is covered with a thin layer of collodion 

 laid on it with a brush. As soon as this layer has somewhat 

 dried, which happens very rapidly, a section is cut and the 

 cut surface is collodionised as before, and so on for each 

 section. This process gives very good results, and may be 

 advantageously employed even with material that has been 

 successfully imbedded, as it gives a better consistency to the 

 tissue, and enables thinner sections to be obtained (VAN 

 GEHUCHTEN, in litt.). 



STRASSEE (Zeit. ivisv. Milt., ix, 1892, p. 8) obtains paraffin 

 sections of 10 cm. breadth by 15 cm. length. He cuts out 

 from hardened material slices of from 1 to 2 cm. in thickness, 

 de-alcoholises them with xylol-carbolic acid mixture, J67, 

 allows this to evaporate, and brings them first into melted 

 yellow vaselin, and lastly either into a mixture of vaselin and 

 paraffin of 42 melting point, or into pure paraffin. 



See also Poso, ih., xxvii, 1910, p. 353 ; DKECKK, loc. rit., 

 742 ; DEJEKine, Anat. Centres Nvrveudj p. '29. 



STRASSEE also imbeds the slices in celloidin, and clears 

 them before cutting with a mixture of xylol-carbolic acid and 

 80 per cent, alcohol in equal parts. 



FEIST (Zeit. wiss. Mile., viii, 1892, p. 492) marks the right and left sides 

 of spinal cord by imbedding with each segment of it a small cylinder 

 (of about 1 square millimetre in section) of hardened liver, stuck verti- 

 cally in the imbedding mass (either celloidin or paraffin) against the side 

 of the cord that it is desired to mark. 



For the freezing method see p. 117, and for further details 

 concerning imbedding and cutting see fourth edition. 



LIESEGANG (Zeit. wiss. Mik., xxvii, 1910, p. 369) mounts large sections, 

 direct from water, in a layer of 5 per cent, solution of gelatin, lets this 

 dry, and varnishes it, dispensing with balsam and cover. 



