1863.] 483 



Owing, however, to the large quantity of molecular matter floating 

 in the serum, and which was coloured by the magenta, difficulties 

 were found in preparing specimens which carried conviction that the 

 macula in question was not an adhering granule. It was also found 

 that it required a nice adjustment of the relative quantities of the 

 solution and of the blood to bring it out. It was only when the 

 right proportions were hit, and especially when the disks were made 

 to roll over in the field of the microscope, that the existence of a 

 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 01 human blood the following par- 

 ticulars were gathered (see fig. 1) : 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. 



A. Human blood. B. Fowl's blood treated with 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. 



