Page:Popular Science Monthly Volume 10.djvu/260

From Wikisource
Jump to navigation Jump to search
This page has been validated.
248
THE POPULAR SCIENCE MONTHLY.

change takes place throughout, making every part more negative. The greatest change is on the external surface of the leaf, immediately opposite to the three sensitive hairs. There is no relation between the preexisting currents and the electrical disturbance consequent on stimulation. The period of latent stimulation (i. e., the space of time occupied by the primary action of the stimulus) is about one-sixth of a second. The period during which the disturbance lasts is about one second. As the leaf becomes fatigued, the period of latency increases to one second and three-quarters, and then most likely the next stimulation produces no effect. The change appears to be a function of the protoplasm of the parenchyma of the region out of which the sensitive hairs arise. Certain of the characters of the change are similar to those presented by muscle and nerve. Why the variation should be a negative one, Dr. Sanderson is unable to determine.

 

New Shells from Colorado.—In the extensive and remarkable display of natural-history objects brought to the Centennial Exhibition by Mrs. M. H. Maxwell, of Boulder, Colorado, was a box of land and fresh-water shells. These have been examined by Mr. Ernest Ingersoll, who made careful studies of the Rocky Mountain mollusks in connection with the United States Geological Survey in 1874, and summarized his results in an article printed in this magazine for May, 1876. Boulder is at the mouth of Boulder Cañon, several miles northeast of Denver, at an altitude of about 5,530 feet above the sea, and on the eastern slope of the main range, where heretofore no shells had been found. The list includes Zonites arboreus, Z. fulvus, Patula Cooperi (living, and very dark and fine), P. striatella, Helix pulchella, Cionella subcylindrica, Vertigo ——? (very minute), Succinea lineata, S. Nuttalliana, Limnea palustris, L. desidiosa, L. humilis, Physa heterostropha, Planorbis bicarinatus, P. tumens, Helisoma plexata, Gyranlus parvus, Ancylus ——?, Goniabasis liveseens, G. pulchella, Sphærium striatinum, Pisidium abditum, and an anodon hardly identifiable.

The collection is remarkable, as coming from the eastern slope of the range, and embracing some unexpected species from east and west. As usual, the Physas are Protean in form, and one can make half a dozen "species" out of them, if disposed. Some of them are well-marked "Inflata." Both the planorbs are reported for the first time from Colorado. P. bicarinatus is a well-known Eastern shell; P. tumens has hitherto been supposed to be confined to Northern Mexico and Southern California. The Helisoma is a new form, discovered by Mr. Ingersoll in an isolated mountain-lake in the southern part of the State, and Mrs. Maxwell finds it at Boulder in a similar situation. Both the Melanians and the Sphærium are additions to the fauna of the State, and the Anodonta will probably prove to be undescribed. Mrs. Maxwell proposes to search still more carefully when she returns, and further information on the geographical distribution of our mollusks in the mountainous territories may be expected from various other quarters where research has been stimulated by the curious results already brought out. Colorado seems to be a meeting-ground for mollusks from all directions, and is a promising field for the collector and student.

 

Marey's Experiments on the Action of the Heart.—Experiments made by Marey show that a diminution of excitability and a rise of temperature in the muscular tissue of the heart invariably coincide with the cardiac systole, while the opposite phenomena are manifested during diastole. The same author has recently attempted to ascertain whether any corresponding variations of the cardiac muscle could be made out. The galvanometer, owing to the inertia of its needle, is unsuitable for the observation of sudden changes in the intensity of currents. Hence, in Marey's experiments, Lippmann's electrometer was employed. The heart of a frog was placed on two unpolarizable electrodes, one supporting the apex of the ventricle, while the auricles rested on the other. Two successive negative variations of the current were indicated by the electrometer during each cardiac systole; one of these was sudden, and corresponded with the abrupt contraction of the auricles; the other was more gradual, and coincided with the slower