366 WM, L. TOWER, 



osmic acid. The tissue was allowed to remain in 1 7o osmic acid 

 until it became brownish; it was then removed, washed in 50 7o al- 

 cohol, and put into 70% alcohol for twelve hours. After being 

 dehydrated it was imbedded in paraffine, xylol instead of chloroform 

 being used as a solvent. Better preparations were obtained, however, 

 if the thoroughly hardened material were cut free-hand in liver or 

 pith, cleared in xylol, and mounted in balsam. 



None of the preparations made by this method, whether imbedded 

 in paraffin or cut free-hand, kept well. Those that were good in 

 June 1896 were of no value a year later, although they had been 

 kept most of the time in the dark, and had never been long exposed 

 to strong light. 



Trials with the methylen-blue method did not turn out very suc- 

 cessfully until near the end of my work. I was able, however, to get 

 some impregnations, which, though in themselves of little use, were 

 of considerable value when taken in connection with the results ob- 

 tained by the use of Vom Rath's method. 



It was with Vom Rath's method that the most satisfactory 

 results were obtained. Although this method does not allow of the 

 isolation of the individual nerve elements, or neurons, it is admirable 

 for tracing nerves, even when they are small and contain but a few 

 fibres. Preparations made by this method are clear and well-defined, 

 although not diagrammatically so, like Golgi and methylen-blue pre- 

 parations. They also show the histological structure of ganglionic 

 cells better than either of the former. 



By this method fair results were obtained even when special 

 care had not been taken in collecting the material, but the best 

 results were those from material collected in the solution described 

 on page 363. A fair staining of Moniezia material was also secured 

 with Vom Rath's mixture when the worms had been collected in a 

 2 7o solution of formaldehyde. Material left in this solution 35 

 days before being placed in Vom Rath's fluid gave very fair results. 

 In this case the stain was darker than when fresh material was used, 

 but not too dark to be of considerable value. It is probable that 

 care in regulating the exposure of such material to the action of 

 Vom Rath's mixture would give a lighter and more desirable stain. 



In using Vom Rath's method fresh material was put into the 

 following Vom Rath's mixture: 



sat. aq. sol. picric acid, filtered . . 500 ccm 

 glacial acetic acid 3 ccm 



