1614 



Journal of Applied Microscopy 



Fig. I. — Photograph of portion of cross section of Hycha showing 

 character of preparation made by the method described. The pho- 

 tograph is much less clear and precise in definition than the prepa- 

 ration. Along the upper left side of the figure the muscle processes 

 may be distinctly seen just at the inner ends of the ectoderm cells. 



in the bottom of a watch-glass with a drop of water just large enough to cover it. 

 If then placed in fairly strong light, as on the stage of a microscope over the 

 opening of the condenser, the animal will soon expand to its full length. Then 



from a pipette filled with the 

 vom Rath mixture a stream 

 of this strong fixing agent is 

 suddenly and forcibly thrown 

 on the Hydra. The speci- 

 men will, provided the stream 

 is directed so as to strike it 

 squarely and is sent with 

 some force, in nearly every 

 case be killed before it con- 

 tracts to any extent. 



Sections are cut five or 

 ten mikrons in thickness, 

 fastened to the slide with 

 Mayer's albumen fixative, 

 and stained by the Heiden- 

 hain iron-hitmatoxylin meth- 

 od. The sections are mordanted about thirty minutes in the iron alum (two 

 per cent, solution), thoroughly washed in water, stained for thirty minutes in a 

 one-half per cent, aqueous solution of haematoxylin, washed again, and difftren- 

 tiated in the iron alum solution. The dififerentiation should be continued till 

 only the nuclei, cell boundary regions, and muscle processes are stained. No 

 counterstain is used. The sections are then carried up through the different 

 grades of alcohol, cleared in xylol, and mounted in balsam. 



The resulting sections are almost diagrammatic in their clearness and are 

 very satisfactory for class use. Such things as the muscle processes, which are 

 ordinarily so difficult of demonstration to students, are so clearly brought out as 

 to cause no trouble whatever. We have appended to this paper a photograph 

 showing, in some degree, the character of the sections prepared in the way just 

 described. Raymond Pearl and Lkwis H. Weld. 



II. The Demojistnxtioii of Nerve Fibers in the Ventral Cord of the Kartlnvonn. 



The following method of making sections of the ventral nerve cord of the 

 earthworm has been found to give preparations which furnish very clear pictures 

 of the structure of nerve cells and their associated axis cylinder processes. The 

 plan was developed with the idea of bringing more forcibly to the student's mind 

 than seems possible with the conventional cross section an adequate conception 

 of the most important structural elements of the nervous system, viz., the gan- 

 glion cells. 



The preparations are made in the following way : Pieces of the ventral cord 

 one and one-half to three centimeters in length are dissected out of a freshly 

 killed worm in physiological salt solution. These pieces are then stretched in 

 small, wax bottomed dissecting pans and held in a straight position by means of 



