G4 



Royal Society : — 



was found therein. When a sohition of tannin, of 3 grains to the 

 ounce of water, was added to blood that had already been dyed with 

 magenta, it was found that the parietal maculse had their colour 

 intensified, and that they became more conspicuous objects. The 

 investigation was, however, not pushed any further in this direction, 

 for it was found that tannin alone produced an even more remarkable 

 effect than magenta. To this effect I now desire to draw particular 

 attention. 



When a solution of tannin, of the strength of 3 grains to the 

 ounce, was applied to human blood, or to that of the horse, ox, 

 sheep, pig, or cat, the blood immediately became turbid ; and when 

 a drop was placed under the microscope the corpuscles were found 

 greatly changed, as represented in fig. 2. 



Each corpuscle appeared to have thrown out a bright, highly re- 

 fractive bud or projection on its surface. The projections were 

 usually about a fourth part of the size of the corpuscle on which 

 they were fixed ; but they varied considerably. Some were only 

 minute bright specks in the cell-wall ; others were half or even two- 

 thirds as large as the corpuscle itself. Very rarely (in mammalian 

 blood) two such projections were seen ; and as rarely a corpuscle 

 was devoid of any. 



The projections were commonly round or dome-shaped, bordered 

 bv a deeply refractive outline. Frequently a minute, apparently 

 vesicular body could be seen within this outline ; and then the pro- 

 jection presented a curiously hooded aspect (fig. 2, b, b). In a uri- 

 nary deposit from a lad twelve years of age, containing pus and blood, 

 nearly every blood-disk presented the hooded appearance after the 

 addition of tannin. 



The blood of the fowl, turkey, duck, and goose showed exactly 

 analogous phenomena with the same reagent (see fig. 3). 



The projection had sometimes the hooded character with a vesi- 



Fig. 3. 



Blood of fowl after the action of tanuin. 



