290 ON A SOLUTION OF UREA UPON THE BLOOD-CELLS. 



most beautiful stellate cells, usually having 3 — 6 tolerably 

 long and somewhat clavate processes, so as to be brought to 

 resemble very closely the irregularly-stellate pigment-cells of 

 the lamina fusca of the sclerotic. This elegant form, however, 

 was not long retained ; for the processes now began speedily 

 to become melted down, sometimes disappearing by a gradual 

 process of fusion commencing at the border of the cell, and 

 occasionally in detaching larger or smaller droplets, which 

 immediately became pale and disappeared. Thus, at last, 

 the nuclear part of the cell only remained as a minute, round, 

 dark-red, brilliant globule, which, ultimately, also lost its 

 colour and disappeared up to the imcleus without leaving a 

 trace. 



In order to ascertain the causes of these extraordinary 

 changes in the blood-cells, 1 began now to try the effect of 

 weaker solutions of urea. These experiments showed, that 

 solutions containing 15 per cent, produced the same changes 

 as those above described, and this was the case also, though 

 more slowly, with solutions containing 12 per cent., or having a 

 specific gravity of about 1 • 043. In solutions of 1 * 026 sp. gr., 

 the cells remained almost without change, whilst in others still 

 more diluted, down to a sp. gr. of 1*004, they were ren- 

 dered spherical and pale, with distinctly-visible nuclei, just as 

 they appear upon the first addition of water. These pheno- 

 mena, as well as the considerations which are opposed to the 

 assumption of a chemical influence being exercised by an 

 indifferent substance, such as urea^ upon the blood-corpuscles, 

 induced me to try the effect of other concentrated solutions 

 upon the blood-cells of the Frog, whence it appeared that in 

 solutions containing 30 per cent, of " sugar of milk," nume- 

 rous blood-cells were rendered so pale, that nothing remained 

 visible except the nuclei. The same thing takes place in all 

 the cells in a concentrated solution of glycerin, except, that in 

 this instance, many of the nuclei exhibit a very delicate border 

 due to the cell membrane. A similar effect follows the ap- 

 plication of mucilage of quince seeds. But in none of these 

 solutions did the blood-cells assume the stellate form, nor 

 exhibit the extraordinary fusion, and breaking up into sphe- 

 rical drops, which is manifested in solutions of xirea ; upon 

 which, however, the less stress, perhaps, should be placed, 

 since human blood-cells, in a solution of urea containing 30 per 

 cent, simply diminish in size, become rounded and lose their 

 colour, without previously exhibiting any other phenomenon. 

 Of salts I have hitherto only tried solutions of common salt 

 and of acetate of soda (Na O A). Wlien concentrated solu- 

 tions of these salts are mixed with frog's blood, and the 



