SCIENTIFIC SUMMARY, 
101 
part immediately after the injury presented sharply-defined irregular bor- 
ders ; after six hours the margins were considerably flattened, so that the 
boundary of the abrasion was much less distinct. After eighteen hours it 
was difficult to tell the seat of the injury with the naked eye, and its 
diameter had become reduced to one-half or one-third ; and after forty 
hours recovery was complete. He convinced himself by microscopic inves.- 
tigation that the process of regeneration, of the epithelium proceeds from 
the margins of the abrasion, the layers of cells immediately bounding the 
seat of injury becoming elongated, and} as it were, sending forth processes 
towards its centre ; so that the margins are rendered very oblique, whilst at 
the same time the exposed surface of the cornea is raised considerably above 
the level of that which is still covered by the cells. These views are dif- 
ferent, of course, but neither can be yet accepted as conclusive. 
A Cheap and Constant Galvanic Battery for Medical Purposes. — Professor 
A. Hammond describes a battery which has recently been devised for him, 
in the New York Medical Journal for November. Each cell contains about 
half-a-gallon of fluid. A disc of sheet copper is laid flat on the bottom of 
each cell. To the under side of this is affixed a copper wire covered with 
gutta-percha. The copper sheet forms the negative plate ; the insulated wire 
wffiich rises to the top of the cell is the positive pole. Two or three inches 
below the upper margin of the cell is suspended by a brass hanger a thick 
disc-shaped plate of zinc, concave on the lower side, with a round aperture 
in the centre. This is the positive plate. To this hanger is attached a 
binding screw, and this forms the negative pole. The body of the battery 
fluid is formed of a solution of sulphate of zinc. Occasionally, as required, 
crystals of sulphate of copper are dropped through the central aperture in 
the zinc to the bottom of the flhid. These dissolve, and produce a layer 
of blue liquid, which covers- the - copper. Thus, we have copper in the 
bottom of the cell, immersed in a solution of copper, zinc suspended above, 
immersed in a white liquid, the solution of zinc. The mode adopted in 
other batteries to separate the fluids- consists m using a porous diaphragm, 
or cup, within, and surrounding which are placed dissimilar metals and 
fluids. The porous septum, it was thought, would allow the-" current to 
pass, and yet prevent the admixture of the diverse elements. It has, 
however, been demonstrated that, when two such liquids, and even two 
gases, are thus separated, they will invariably become mixed. In this 
battery, without the intervention of any diaphragm, the denser liquid, the 
blue, remains in the bottom of the cell, the lighter one overflows and- rests- 
upon it ; thus arranged, there is less liability to diffusion or mixing than 
if the two liquids were placed side by side, in vertical columns, with a 
porous partition between them. The central aperture in the zinc plate 
also admits the introduction of a hydrometer to measure the density and 
strength of the liquid. Provision is also made for preventing too rapid 
evaporation of the fluid. The occasional addition of a little water, 
and every three or four days dropping in a few crystals of sulphate of copper, 
is nearly all that is required in the management of this battery. 
