xxx THE BLOOD. 



to plasticity of its substance ; and the case has been compared to the section 

 of a soap-bubble into two or more without destruction or collapse. Dr. W. 

 Roberts,* who makes this comparison, has brought forward some curious 

 observations on the effects of solutions of magenta and of tannin on the 

 corpuscles of man and various animals, which seem to him to speak for the 

 presence of an envelope. It must, I think, be admitted that the question is 

 open to debate, but it could not be settled by even a much more extended 

 discussion than could suitably be introduced here. 



The distension by water is caused by the thinner exterior fluid passing by 

 endosmosis into the thicker matter of the corpuscle ; and precisely the opposite 

 effect may be produced by immersing the corpuscles in a fluid of a sufficiently 

 high degree of concentration, so as to cause the predominant current to pass 

 from within outwards. Accordingly, on using a strong solution of salt or of 

 sugar, the corpuscles will shrink and become thinner ; and, no doubt, the 

 variations in plumpness which they often naturally present, are owing to 

 differences in the degree of concentration of the surrounding liquid. The 

 nucleus (fig. xvi., 3 ) is rather more than a third of the length of the cor- 

 puscle ; it appears, especially after being exposed to the action of vinegar, 

 to be composed of tolerably large granules, and, when FO treated at least, it 

 is quite free from colour. But it must be remembered that it is only after 

 exposure of the corpuscles that a nucleus becomes apparent ; nothing of the 

 kind is observable when they are seen within the vessels, so that some think 

 the nuclei are formed by a sort of precipitation or consolidation in the 

 substance of the corpuscles when they are withdrawn from the animal. The 

 envelope is supposed to be an exceedingly fine, homogeneous, and pellucid 

 membrane. The coloured content of the corpuscle is a pale reddish matter ; 

 not liquid, but obviously of a soft and yielding nature, for the corpuscles 

 alter their shape on the slightest pressure, as is beautifully seen while they 

 move within the vessels ; they are also elastic, for they readily recover their 

 original form again. It must be remarked that the blood-corpuscles when 

 viewed singly appear very faintly coloured, and it is only when collected in 

 considerable quantity that they produce a strong deep red. 



A structure similar to that shown in the large blood-disks of amphibia, 

 may be demonstrated in many other instances, and by analogy has been 

 inferred to exist in all, man not excepted. But although the blood-cor- 

 puscles of man and mammalia are nucleated in the early stages of their 

 formation, it is now satisfactorily established that in their perfect or final 

 condition they are destitute of nuclei. As to an envelope, some observers, 

 who admit its presence in the red corpuscles of oviparous vertebrata, doubt 

 its existence in mammalian blood-disks. From long continued and 

 careful observation, Mr. Gulliver concludes that the mammalian red cor- 

 puscle consists of two parts ; viz., 1, a tegumentary membranous frame of 

 colourless, homogeneous, structureless substance, containing, 2, a semi- 

 fluid, viscid, coloured matter. The effect of water is to extract the easily 



* Proceedings of the Royal Society, vol. xii. p. 481. Hensen, who also holds to the 

 belief of an envelope, thinks that the red corpuscle of the frog contains protoplasm in a 

 layer next the envelope, and also round the nucleus, and elsewhere a coloured intra- 

 cellular fluid. His observations show that the contents may be separated into two 

 substances, but they are by no means conclusive as to the alleged natural distribution of 

 these substances within the corpuscle. (Zeitschr. fur wiss. Zoologie, 1861, p. 263.) 

 For some interesting observations by Dr. W. Addison, F.R.S., on the curious effects 

 produced on red blood-corpuscles by immersion in sherry-wine, see Proceedings of the 

 Royal Society, Dec. 8, 1859. 



