62 Royal Society : — 



coloured particle organically connected with the cell-wall could be 

 satisfactorily made out. The best specimens were prepared from 

 human blood drawn in the fasting-condition, and from the blood of 

 a kitten two days old. 



From well-prepared specimens of human blood the following par- 

 ticulars were gathered (see fig. 1, A) :— Nearly every disk possessed 

 the parietal macula ; it could be distinctly recognized in nine-tenths of 

 them ; and in several of those in which it was not at first visible, it 

 came into view as the corpuscles revolved in the field. 



Fig. 1. 





« V ^^ J ^ 



A. Human blood ; B. Fowl's blood, treated witb magenta. 



The macula was clearly situated in the cell- wall, and not in the 

 interior of the corpuscle. Usually it appeared as if imbedded or set 

 in the rim of the disk, like the jewel in a diamond ring ; but some- 

 times it occupied various positions on the flat surfaces, and when 

 so placed, the spot was difficult or impossible to detect. 



It commonly presented a thickly lenticular shape ; sometimes it 

 was square, and occasionally in appearance vesicular (fig. 1, A, a). 

 In some instances, and especially in long-kept specimens, the particle 

 was seen to stand out on the outline of the disk like an excrescence. 

 Still more rarely, instead of a spot, a thick red line ran round the 

 circumference for a quarter or a third of its extent (fig. 1, A, b). 



As a rule it was extremely minute, covering generally not more 

 than a twentieth or thirtieth of the circumference ; but there v/as a 

 considerable variation in its magnitude and distinctness. Very rarely 

 two specks could be seen ; but the occurrence of adhering granules 

 rendered the verification of this point extremely difficult. 



This description applies, so far as the inquiry has yet been prose- 

 cuted, to the mammalian blood-disk generally, making allowances 

 for differences in size. In the camel the macula occupied indiffer- 

 ently any part of the oval outline. 



Among the oviparous classes, the blood of the fowl, frog, dace, 

 and minnow has been most fully examined (see fig. 1, B) ; but the 

 blood of the sparrow, duck, goose, and turkey was also searched, as 

 well as that of the newt and carp. 



In all of these a tinted particle appeared, more or less constantly, 



