Royal MicrosGO])ical Society. 53 



clear and sharply-defined double-contoured cells by a very weak 

 solution of chromic acid, while the younger specimens remain 

 totally unaffected. Among the small veins of human embryos that 

 have been lying in such a solution, many examples are met with, 

 in the interior of which the coloured blood corpuscles, arrested 

 and accumulated by the death of the embryo, have assumed an 

 hexagonal form, and appear, in consequence of the action of the 

 chromic acid solution, here as clear double-contoured hexagonal 

 cells ; they may thus give rise to serious errors. Even in the 

 blood of adults a number of coloured corpuscles are frequently 

 observed, which resist more or less the influence of one or the 

 other reagent. This fact, in connection with those above men- 

 tioned, seems to indicate that the chemical composition of these 

 bodies is not the same in all periods of their life. 



These observations show that, under certain circumstances, the 

 coloured blood corpuscles may appear in the form of double-con- 

 toured cells. The question arises, therefore, whether this double 

 contour is an artificial production, or whether it really represents 

 a distinct j^art of the fresh blood corpuscle. In those cases where 

 the reagents used were acids, it may be alleged that, while by 

 their action the superficial portion of the blood corpuscle, to a 

 certain depth, was rendered more dense, the water of the solution, 

 at the same time, dissolved the inner portion, resulting in the 

 production of an artificial double-contoured cell. This explanation, 

 however, could not be applied to those cases where an entirely 

 neutral agent, as water, was used. The double contour, therefore, 

 must evidently depend upon some other cause. Might it not be 

 that the coloured blood corpuscle of man, when it arrives at 

 maturity, undergoes a shght condensation on its surface, in the 

 form of a thin layer or pellicle, which, resisting the solving power 

 of the water, would finally appear in the form of a double contour. 

 This explanation has been, if I remember rightly, advanced before, 

 and seems to be more plausible than to deny to the blood corpuscle 

 the existence of an enveloping membrane altogether. It is, more- 

 over, supported by the fact which I have stated above, namely, 

 that the younger embryonic blood corpuscles remain unafiected 

 when coming in contact with a weak solution of chromic acid, 

 while on the older ones a double contour makes its appearance. 

 There are other facts which I have observed in support of the 

 existence of an enveloping membrane on the human blood cor- 

 puscle, the statement of which I must, however, postpone to a 

 later period. I beg to state here that, regarding this subject, I have, 

 in the coui'se of this year, made a series of close examinations on those 

 giant blood corpuscles of AmpJiiuma means [? Astridadylum, Ed.] 

 vulgarly called "conger eel," and also on the frog, the results 

 of which indicate the existence of a membrane. As, however, the 



