484 [March 19, 



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, 6). 



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

 than a twentieth or thirtieth of the circumference ; but there was 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, 

 in the cell- wall, when the corpuscles were treated with magenta*. 

 The presence of a central nucleus in these classes caused the ma- 

 cula to be invisible more frequently than in mammalia, inasmuch as 

 it suffered eclipse when situated over or under the central nucleus. 



In the fowl, dace, and minnow it was found easy to bring out the 

 parietal macula ; in the fish two spots were not unfrequently seen. 

 The macula was situated indifferently on any part of the periphery ; 

 and sometimes it projected from the surface. When happily pre- 

 pared the specimens were even beautiful. The central nucleus was 

 dyed of the finest red ; and on the delicate outline of the cell-wall 

 hung the red parietal macula, offering a not altogether fanciful re- 

 semblance to the astronomical figures representing the moon coursing 

 in its orbit round the earth. 



At this stage of the inquiry it was conceived that an improved 

 demonstration might be obtained by fixing the dye with a mordant, 

 and then subjecting the corpuscles to a lavatory process, so as to get 

 rid of the floating granules which so much interfered with the view. 

 For this purpose a solution of tannin (which is one of the mordants 



* In order to bring out the best results, it was found requisite to modify the 

 strength and quantity of the 'solution for the different kinds of blood. This 

 doubtless depended upon the varying densities of the liquor sanguinis and cell- 

 contents in different animals. 



