No. 637] SHORTER ARTICLES AND DISCUSSION 179 



The slide with all three kinds of sections was stained for 12 

 hours in alumcarmine, a stain which, as is well known, does not 

 overstain. They were then washed in water and again stained 

 for 12 hours in a weak alcoholic solution of Bleu de Lyon. All 

 sections on this slide received therefore the same treatment and 

 the difference in the depth of stain was entirely due to the thick- 

 ness of the section stained. 



The other slides were treated in a different way. They were 

 stained in Delafield's haematoxylin followed by tetrabromfluo- 

 reseic acid. This stain was chosen because it is possible at will 

 to control the depth of staining. A set A of three slides, one 

 with 5 micromillimeter sections, one with 10 and one with 20, 

 was treated simultaneously in a Coplin's staining jar. The sec- 

 tions were therefore stained, washed, destained in acid alcohol, 

 treated with ammonia alcohol, stained in a weak solution of 

 tetrabromfluorescic acid in 95 per cent, alcoliol iuid washed in 

 pure alcohol the same longth of time. In re.srard to depth of 

 stain these slides presented, tlierefore, tlie same conditions as the 

 slide stained in alumcarmine and Bleu de Lyon. 



Several other slides were treated individually in the same 

 stains. They were all first considerably overstained in Dela- 

 field's h£ematoxylin, washed in Avater and destained in acid 

 alcohol until they had when viewed over a white surface, the 

 same shade of eolor to the naked eye, regardless of the thickness 

 of the section. If after treatment with ammonia alcohol the blue 

 color was not approximately of the same shade, the darker slide 

 was again transferred to the acid alcohol, until all sections 

 looked approximately alike. They were now stained in the 

 tetrabromfluorescic acid, the thickest sections remaining a short 

 time in the fluid, the 10 micromillimeter sections somewhat 

 longer and the 5 micromillimeter sections longest, and again 

 compared over a white surface. From several slides thus pre- 

 pared three were selected which to the naked eye were to all 

 purposes of the same appearance, although their respective 

 thickness were 5, 10 and 20 niicroniilliineters. Hero then we 

 had a Set B of sections in which the depth of stain had uothinu^ 

 to do with the thickness of the seetioti, but was nitirt'ly ilfp.'ud- 

 ent upon the amount of stain absorbed by the tis^surs. 



Frartional cxposuivs on oil honor, plat.'s w itli ( 'nimor ray- 



ratus^uul'\l.''vel(>p^ by ,h!' tiuu- a.ui trinperanu-.. ni'thod with 



