256 MRS. ERNEST HART. 



edge exactly overlaps the metal eyelet ; a screw fitting the eyelet 

 is then inserted into the hole^ and the method of procedure is as 

 follows : — The tip of the finger is pricked and a drop of blood is 

 placed, as rapidly as possible, at one of the free edges of the 

 cover glass ; the blood enters by capillary attraction, forming a 

 delicate even layer between the two glass surfaces ; the slide is 

 then inverted over a shallow vessel containing a 2-per cent, 

 solution of osmic acid, and the hinged cover glass is gently 

 raised by passing the screw furtlier through the eyelet. All the 

 fluid particles, and the great majority of the corpuscles, flow 

 immediately towards the hinged edge of the cover glass, leaving 

 only a few red corpuscles, and here and there a white one, ad- 

 hering to the glass surface ; these are indantaneously fixed by 

 the action of the osmic acid vapour — a fact originally pointed out 

 by Professor Ray Lankester many years ago — indeed so perfect 

 and complete is the fixing of the corpuscles on the glass by the 

 action of the osmic acid vapour, that the glass may be immersed 

 for a long time in water, and may even be dried roughly with a 

 towel without displacing or injuring them. Among the cor- 

 puscles which have adhered to the glass surface. Dr. Norris 

 discovers, by various means of staining, his invisible corpuscle. 

 That it is there I do not deny, but that it is there because it 

 previously existed in this condition in the blood in the living 

 state is I think open to dispute ; in fact,as I stated in my former 

 paper, these colourless discs are in my opinion unstable red cor- 

 puscles, or corpuscles of low resistance, which have parted with 

 their haemoglobin, possibly simply by the fact of the withdrawal 

 of the serum. 



In continuing these investigations and in repeating this 

 experiment of " isolation " a great number of times, T began to 

 observe that the appearances changed according to the length of 

 time which elapsed between the spreading of the layer of blood 

 between the two glass surfaces and the moment when the cover 

 glass was raised; and thus discovered that a whole series of 

 phenomena could be traced, leading from the pale or colourless 

 corpuscle up to the complete formation of networks or bands of 

 fibrine. In developing this method of working I found that the 

 staining reagents recommended by Dr. Norris were not sufficiently 

 powerful to bring out all the details that could be observed on 

 the glass surfaces, and after many trials I found that a highly 

 concentrated solution of nitrate of rosanilin in absolute 

 alcohol was the best staining reagent to use. The method I 

 adopted was to detach the cover glass from the slide after the 

 corpuscles had been fixed by the osmic acid vapour, and to 

 examine both the surfaces of the cover glass and the slide 

 under the microscope, to see which presented the most perfect 



