66 Royal Society : — 



blood-disks the application of acetic acid, soon after the tannin, 

 caused, on two occasions, the puUulations gradually to subside, and 

 finally to disappear ; and then the disk resumed its original circular 

 outline. I failed to produce this " redux " effect in the fowl ; and 

 did not always succeed with human blood, probably because the 

 change produced by the tannin had gone too far. 



The modification noted under the term "hooded" appearance 

 depends, I believe, upon secondary conditions of concentration and 

 quantity of the tannin-solution in comparison to the blood. When 

 the hooded condition has been watched in the act of occurrence, it 

 was noticed that the outer hood was shot out^r^^; and instantly after 

 this the highly refractive vesicular body made its appearance within. 

 The contents of the hood (excluding the vesicular body) appeared 

 usually to refract the light like the body of the cell, or even less 

 strongly ; sometimes, however, more strongly. 



The effect of tannin did not cease with the production of the ele- 

 vations just described. At first the cells and their projections pre- 

 served their elasticity ; but after a while (a few minutes, or several 

 hours, according to the proportions used) the corpuscles and their 

 projections became solid, and they could be cracked by pressure 

 under the microscope like starch-granules. More slowly the same 

 destruction overtook the corpuscles spontaneously ; and this signifi- 

 cant fact was observed in the course of it : — sometimes the cell 

 ruptured before the projection, the latter persisting as a bright 

 granule amid or near the debris ; sometimes, on the other hand (in 

 the horse), the projection broke up before the disk to which it was 

 attached. In this latter case, the hood (if there were any) broke up 

 first into a scattered nebula of granular appearance, and then the 

 nucleolus-like body within burst into three or four bright fragments 

 (fig. 2, d). This train of events seemed to remove all doubt as to 

 the complete isolation of the projection from the cavity of the disk. 

 Last of all, the disk itself began to crack ; in a few days all my spe- 

 cimens were thus destroyed. 



In addition to magenta and tannin, the following substances were 

 tried, but they did not produce phenomena in the least analogous with 

 the foregoing: — gallic acid, ferrocyanide of potassium, santonine, 

 sulphate of magnesia, alcohol and water, solutions of carbolic acid, 

 of atropine, morphia, iodine, sugar, gum, glycerine, and infusion of 

 coffee. 



A solution of picric acid produced the appearance of a parietal 

 particle like that brought out by magenta, except that it was not 

 coloured. An exactly similar appearance was on one occasion ob- 

 served in blood-corpuscles in the urine of a patient with acute Bright's 

 disease. 



When magenta was applied after the process of pullulation had 

 taken place, the projections were found to take the dye strongly, and 

 especially the vesicular body within the hood. By this proceeding 

 beautiful and remarkable objects for microscopical examination were 

 obtained. In the fowl, dace, and minnow the projection was tinted 

 earlier than the central nucleus — probably from its more ready access 



