Journal of Applied Microscopy. 279 



washing out of the acid is not necessary, ahhough it will do no harm. The 

 object may be mounted directly in gum syrup or in concentrated glycerin. 

 There is danger of shrinking the material in the dehydrating and clearing neces- 

 sary for mounting in balsam. The characteristic reaction may be obtained in 

 material that has been dead for some time, or after maceration in a one-third 

 solution of alcohol for a day. Fine preparations, showing the end branchings of 

 the nerve in isolated plates of the electric organ of Torpedo, may be obtained in 

 this way. 



The second method : Invertebrate tissue is fixed in a concentrated solution 

 of sublimate in one-half per cent, sodium chloride ; or in sublimate alcohol 

 which consists of equal parts of the above solution and absolute alcohol. If 

 it is specially desired to show the outline of the cell, a fluid consisting of equal 

 parts of the sublimate solution and one per cent, osmium tetra-oxyd may be 

 used. This is also preferable for vertebrate tissue. Large pieces of tissue 

 are left in the sublimate alcohol from sixteen to twenty-four hours, thin mem- 

 branes from four to five hours, or half that time in sublimate. The osmium 

 solution is used like the others except that it requires washing in running water 

 for six hours, and the steps preliminary to imbedding should involve the least 

 possible exposure to light. After fixing, the object is washed in a solution of 

 one per cent. KI and one-half per cent. I in water. Wash for from six to eight 

 hours, frequently renewing the liquid, then bring the material directly into 

 95 per cent, alcohol, and leave over night; change to a solution of one per 

 cent. KI and one-half per cent. I in 95 per cent, alcohol, until it is thoroughly 

 yellowed, when the iodine is washed out with absolute alcohol. Objects thin 

 enough to be transparent without sectioning are not placed in alcohol, but 

 washed in the iodine solution. The quicker the material can be imbedded after 

 fixing, the more successful the action of the gold chloride will be. Chloroform, 

 or a solution of four parts of chloroform and one part ether, should be used 

 in preference to xylol for clearing. Imbed in parafiin or celloidin. From seven 

 to ten micra is the best thickness for sections. Fix the paraffin sections to the 

 slide with distilled water, or with albumen fixative, the celloidin sections by the 

 bergamot oil method. Remove the paraffin with chloroform, and bring the sec- 

 tions, by the usual steps, to distilled water, where they are left for at least two 

 or, at most, six hours. Or, they may be rinsed in distilled water, then placed in 

 a one per cent, solution of formic acid for a moment, and rinsed again in water. 



The slide is then placed in a tube of one per cent, gold chloride for twenty- 

 four hours, or at least over night. Dip the slide quickly in distilled water or 

 remove the superfluous gold chloride from the glass (not from the sections) with 

 filter paper, and immerse the slide in a glass tube of one per cent, formic acid, 

 placed where it will receive the maximum of light on all sides, with the minimum 

 of heat. The slide should be placed obliquely with the sections on the under 

 side, where they will be protected from the precipitate which forms. After 

 twenty four hours rinse in distilled water and mount in the usual way in balsam, 

 or directly in concentrated glycerin or gum syrup. 



For either method, the most important condition is that the light rays shall 

 reach the tissue on all sides, and penetrate it with the greatest possible intensity 



