mVERTEBRATA., CRYPTOGAMIA, MIOROSCOPy, ETC. 231 



ttat, if th« refractive index of the serum be changed by means which 

 are conservative and not destructive of the integrity of the red cor- 

 puscles, the transparent or third corpuscle cannot be found by any of 

 the ordinary methods of observation. 



Regarding the method of " packing," the corpuscles are here 

 subjected to an extreme degree of pressure. They are drawn by the 

 force of capillary attraction between two glass surfaces bound firmly 

 together, until they reach a spot which they cannot pass by reason of 

 the close contact of the two glasses. They therefore become wedged 

 in and are subjected to the action of two forces, the capillary attraction 

 which is drawing the liquor sanguinis from around them, and the 

 pressure of the glasses between which they are tightly wedged. This 

 pressure causes certain of the corpuscles to discharge their haemo- 

 globin and to become transparent. Some of the corpuscles are acted 

 on in this way much more rapidly than others ; but in course of time 

 a great number of the corpuscles become quite colourless, and all of 

 them as they pass towards the centre of the glass, where the pressure 

 is greatest, become paler. Moreover it may be observed that at the 

 same time the serum becomes distinctly tinted on the further side of 

 the Newton rings, and in one instance Mrs. Hart determined by the 

 micro-spectroscope the presence of the discharged haemoglobin in the 

 serum. 



While the " isolation " method is the one least open to objection, 

 Mrs. Hart thinks that the capillary attraction of two glass surfaces 

 with a thin layer of fluid between them, and the amount of force 

 necessary to overcome this attraction and raise the cover-glass, have 

 not been sufiSciently considered, nor the probable effect of violence 

 done to the delicate structure of the red blood-corpuscles by the 

 antagonistic forces here brought into play. Many of the corpuscles 

 have the appearance of being ruptured, and of having lost their 

 contents. On repeating the same experiments with frog's blood it 

 was found that either the corpuscles were ruptured, setting their 

 nuclei free, or were rendered transparent by the loss of htemoglobin ; 

 in fact, the appearances produced by isolation are identical with those 

 eflfccted by the well-known experiment of pressure on the cover-glass 

 over a fresh preparation of frog's blood. It may bo noticed, however, 

 as a i)oiut in favour of this method, that the small metal eyelet 

 prevents the glasses from being in such close apposition as might be 

 6uj>i)()scd, and lioncc the cai)illary attraction is not as powerful as it 

 wcnild Ijo if the glasses were in close contact. In this method also, 

 the possible effect of the sudden withdrawal of tho liquor sanguinis on 

 the more uustjiblo of the corpuscles is a point not to be lost sight of. 



Finally, regarding Dr. Norris's tlieory as to tlie alleged false 

 ai)peariinco of nucloation in tlie lyniph-corpusclcs and the wliite blood- 

 corpuscles, M. lianvicr's observations* concerning the division of the 

 nucleus of the living wliito blood-corpuscle in the Mcxiwiu axoloti 

 may bo referred to. Owing to the transiiurtiicy of tbe prDtDjilasm, 

 tho nucleus and tho nucleolus are distinctly visible in the living 



♦ ' licchcrcbca aur lea Elemenla dn Sung.' Ijibl. Iiautcd Etiulcd. I^bor. 

 dHibtolo^io. 



