210 Histology of Minute Blood-vessels, — [Mgnthly, Microscopical 
by Wales’s 3th objective, illuminated by the magnesium lamp. The 
preparation was made by Dr. J. C. W. Kennon. 
The principal venous trunk represented in this photograph is 
ahoth of an inch in diameter. It is formed by the union of three 
smaller radicles, of which that on the left hand is much out of focus. 
Another smaller radicle, also much out of focus, joms the trunk on 
the left, near the bottom of the picture. The walls of the venous 
trunk, and of those of its branches which are in focus, are plainly 
seen to be formed of somewhat irregular epithelial cells, which vary 
in shape and size, averaging =}oth of an inch in length and zs/opth 
in breadth. The boundary of each cell is indicated by a zigzag 
black line. In each of the cells which is accurately in focus, a 
smooth, oval nucleus, 355th of an inch in length is visible. In 
examining the original preparation, by changes in the fine adjust- 
ment of the microscope, similar nuclei can be seen in each of the 
epithelial cells. These nuclei, being brilliantly stained with carmine, 
contrast sharply with the black cell-boundaries resulting from the 
silver imbibition. By a still further alteration of the fine adjust- 
ment, the cells and nuclei of the opposite side of the vein are brought 
into view. 
In the tissue external to the vein, two kinds of nuclei are shown 
in the photograph. The first are narrow and elongated, averaging 
about y;59th of an inch in length and 5,5,th in breadth. These 
are the nuclei of the fibre-cells of the muscular coat of the bladder. 
The fibre-cells themselves are not shown in carmine stainings, but 
are readily demonstrated in fresh preparations by the action of solu- 
tions of osmic acid or of chloride of gold. Indications of the mus- 
cular bands formed by the union of these fibre-cells are, however, 
seen in the photograph, particularly on each side of the principal 
venous trunk. The second variety of nuclei are oval, about sth 
of an inch long, and belong to the connective tissue of the bladder. 
The cells in which these nuclei lie are not seen, the action of the 
carmine being limited to the nuclei. They can, however, readily be 
demonstrated in fresh preparations by gold-chloride and some other 
reagents. The cut represents the outlines of a portion of the 
photograph ; a, a, are the nuclei of the vascular epithelium; 8, b, 
the nuclei of the muscular fibre-cells ; ¢, c, those of the connective 
tissue. 
III. Sketch of a photograph representing the stomata between 
the epithelial cells of a vein 5th of an inch in diameter in the me- 
sentery of the frog. Negative No. 40, New Series. From prepara- 
tion No. 3276, Microscopical Section. Magnified 400 diameters 
by Wales’s 3th objective. The preparation was made by myself. 
Owing to the curved form of the vein, but a small portion of its 
surface is in focus. In this portion the silver-stained boundaries of 
several of the epithelial cells of the vein are visible, and display in 
