1885. | Microscopy. 527 
system with a thin colored injection mass, as in making an ordi- 
nary injection. When this has passed through the capillaries and 
well filled the veins, there is forced into the artery a differently 
colored Plaster mass which pushes the previously injected thin 
mass before it until the plaster has reached the capillaries, where 
its onward movement is arrested. For a year or more before 
Osborn’s notice was published, double injections based on the 
same principle had been made by the writer. As practiced by 
myself, a canula was fitted into the aorta of a cat, and a gelatine 
mass colored with carmine was injected until it was seen to flow 
from the right side of the heart; then the tube conveying the red 
mass being detached, a tube conveying a blue gelatine mass was 
slipped over the same canula, and the pressure again applied, 
Into this blue mass had been mixed thoroughly a quantity of 
starch, preferably from wheat. This starch-bearing mass pushed 
the carmine mass before it until the starch grains entered the 
capillaries and effectually plugged them up. The arteries were 
thus left blue and the veins red, and so well was the work accom- 
plished that a lens of considerable power had to be used to dis- 
cover any admixture of the colors in the smallest vessels of thin 
membranes. The first mass injected need not be unusually thin. 
The capacity of the capillaries is so great, as compared with 
that of the arteries, that any commingling of the two colors is 
concealed in them. Carmine is used for the veins because of the 
ease with which it may be prepared, its permanence and the facil- 
ity with which it passes through the capillaries. On the other 
hand, the gelatine for the arteries may be colored with the coarser 
pigments, such as Prussian blue or ultramarine. The latter fur- 
nishes a beautiful blue. Vermilion is not suitable for the first 
injected mass, since on account of its high specific gravity it 
readily sinks to the lowest side of the vessels, drags behind, and 
causes a commingling of the colors. An additional reason for 
filling the veins with red rather than with blue is found in the 
agreeable and natural color given to the preparation. 
Of course a mass of plaster of Paris injected after a gelatine 
mass will drive it until the plaster reaches the smallest vessels, 
thus producing a double injection. e st h mass recently 
proposed as a filling for blood-vessels will readily lend itself to 
the production of a double injection according to the method de- 
tailed above. 
III. A method of producing double injections for histological 
purposes.—So far as I am aware the usual method of producing 
that the mass is entering the capillaries, and immediately after to 
inject a differently colored mass into the vein. The injection be- 
