60 PRACTICAL HISTOLOGY. 



the two with the point of a needle, and cover. No nucleus 

 is revealed in the coloured corpuscle, but in the white 

 corpuscle three nuclei usually appear. 



82. Effect of Tannic Acid. Add to the same blood 

 a drop of tannic acid solution ( 7 6). Mingle the two with 

 the point of a needle; cover, and examine immediately. 

 The coloured corpuscles undergo a change similar to those 

 noticed in the newt's blood. Frequently, however, a deli- 

 cate envelope may be seen outside the bud of extravasated 

 haemoglobin. 



83. Structure of the Blood Corpuscles. In all 

 animals the white blood corpuscles are nucleated masses of 

 protoplasm without any apparent envelope. The coloured 

 corpuscles are nucleated in fishes, amphibians, and birds, 

 but not in mammals ; and it is to be observed that the 

 mammalian corpuscle comports itself towards re-agents not 

 like the nucleus, but like the perinudear portion of the 

 nucleated coloured corpuscles. Notwithstanding the con- 

 trary opinion of Rollett (Strieker's Histology, i. p. 408), we 

 maintain with Hensen (lib. at., p. 409) that the coloured 

 corpuscles have an envelope. The membrane can be 

 distinctly seen with a power of about 1000 diam. in the 

 newt's corpuscle after the addition of magenta and tannic 

 acid. In the mammalian corpuscles it is difficult to form 

 a decided opinion from direct observation, but the be- 

 haviour of the mammalian corpuscle towards re-agents is so 

 similar to that of the newt's corpuscle, that the existence of 

 a membrane in the former may be safely inferred. The 

 haemoglobin lies between the nucleus and the envelope. 

 All that is to us perfectly clear, but the remainder is 

 doubtful. Rollett maintains that the pigment fills the 

 interstices of a colourless sponge-like stroma. Hensen 

 (quoted by Rollett) states that he has seen a system of 

 extremely delicate filaments stretching from the nucleus of 

 the newt's corpuscle outwards to the envelope. Whether 

 or not this sponge-like or thread-like stroma is present it 

 would be difficult to say, but its existence would assist us 

 in comprehending how the non-nucleated human corpuscle 

 so definitely and regularly maintains its biconcave shape. 



