1889.] Physiology. 275 
the spinal cord affects the staining qualities of the cells. In 
the frog the sciatic plexuses are laid bare, the nerves are cut, 
and the central end of the eighth nerve is stimulated at regu- 
lar intervals for one hour, each stimulation of three minutes 
being followed by a rest of two minutes. The spinal cord is 
then removed, hardened, sectioned, and double-stained with 
haematoxylin and safranin. For a control experiment the 
spinal cord of another frog is, in each case, prepared in ex- 
actly the same manner, with the exception of the nerve 
stimulation. An active and a resting cord are thus obtained 
for comparison. The nuclei of the cells of the grey matter 
are colored — some red and some blue-violet. Enumerations 
give in the control (resting) cord to i red, 8.97 blue nuclei ; 
in the stimulated cord to i red, 2.71 blue ; in the active cord 
the relative number of red is 3.31 times greater than in the 
resting one ; in parts of the cord lying immediately adjacent 
to the entrance of the stimulated nerve, the red nuclei are 
relatively even more abundant. The chemical condition of 
the nuclei is evidently altered so as to make them more sus- 
ceptible to the safranin than to the hematoxylin. [It is to 
be regretted that the author apparently enumerates all the 
cells, even those of the supporting tissue, with the nerve 
cells.] 
Gaseous Exchange in the Lungs.— Professor Bohr, of 
Kopenhagen, has recently carried on a series of experiments, 
the results of which indicate the incorrectness of the com- 
monly received opinion that the passage of oxygen and car- 
bonic dioxide between the air and the blood in the lungs is a 
process of simple diffusion.* By a modification of Ludwig's 
stromuhr the blood of the carotid artery of a dog was, in its 
passage, exposed to the air of a closed chamber until equilib- 
rium had been established between the blood and the air ; 
the latter was then analyzed, and the partial pressures of the 
gases determined ; these partial pressures represent the ten- 
sions of the same gases in the blood. The tensions of the 
gases in the expired air were determined at the same time. 
In nearly all cases in the blood the carbon dioxide tension 
was found lower, the oxygen tension higher, than in the ex- 
pired air. The results would have been still more striking, 
could the air of the pulmonary alveoli have been used, since 
there the CO, tension is necessarily greater, the O tension 
less, than in the expired air. The experiments indicate that 
each gas, in passing through the alveolar and capillary walls 
passes from a place of low to one of high tension, a fact which 
' Centralblattf. Physiologie, 1887, p. 293, and 1888, p. 437- 
