Page:Popular Science Monthly Volume 21.djvu/433

Rh sharp, sudden detonation of nitro-glycerine is calculated to generate shorter waves than a more deliberate explosion. This view is confirmed by the fact that, when an extremely disastrous explosion of nitro-glycerine took place in San Francisco in 1880, a violent concussion was felt in the University buildings, three miles away, while no aërial shock was felt at Professor Joseph Le Conte's house, eight hundred and ninety feet farther off, but within the geometrical shadow of one of the buildings. The sound-wave coming by the air was completely cut off by the acoustical shadow cast by the intervening: structure. This would not have been the result in the case of ordinary sounds.

The Salmon-Disease.—Professor Huxley recently read a paper before the Royal Society on the disease which prevails occasionally among the salmon in North America and Siberia, in which he reviewed the results of the commission that was appointed in 1878, when the disease raged in the Solway district, to investigate its nature. The evidence taken before the commissioners leaves no doubt that the malady is to be assigned to the diseases caused by parasitic organisms, and that it is a contagious and infectious disease of the same order as ringworm, the muscardine among silk-worms, and the potato-disease, and is the work of a minute fungus. In fact, the Saprolegnia which causes it is an organism closely allied to the Peronospora, which is the cause of the potato-disease. One distinction may be marked between them, that the Peronospora are parasites depending altogether upon living plants for their support, while the Saprolegnia are essentially saprophytes, that is, they ordinarily derive their nourishment from dead animal and vegetable matters, and are only occasionally parasites upon living organisms. The zoöspores of these plants, diffused through the water, germinate and produce a mycelium similar to that from which they started as soon as they reach the healthy skin of a salmon. Professor Huxley experimented in inoculating the bodies of dead house-flies from the diseased salmon-skin, and in a few hours saw the bodies completely taken possession of by the white filaments of the fungus; it was proved to him that the pathogenic Saprolegnia of the living salmon may become an ordinary saprogenic Saprolegnia, and, per contra, that the latter may give rise to the former. Hence the cause of salmon-disease may exist in all waters in which dead insects infested with the Saprolegnia are met with. The Saprolegnia do not appear to be found on decaying bodies in salt-water. We must, therefore, "look for the origin of the disease to the Saprolegnia which infest dead organic bodies in fresh waters. Neither pollution, drought, nor over-stocking, will produce the disease if Saprolegnia are absent," although they may favor the conditions on which its spread depends. Professor Huxley also concludes that the chances of infection for a healthy fish entering a river are prodigiously increased by the existence of diseased fish in that river, insomuch as the bulk of Saprolegnia on a few diseased fish vastly exceeds that which would exist without them. Hence, "the careful extirpation of every diseased individual is the treatment theoretically indicated; though, in practice, it may not be worth while to adopt that treatment."

Catalogue of Scientific Periodicals.—Dr. H. C. Bolton, of Trinity College, is preparing for the press his long-delayed "Catalogue of Scientific Periodicals," which will appear in the octavo series of the Smithsonian Institution. The catalogue is intended to embrace independent journals of pure and applied science, published in all countries, from 1665 to 1880; so far as possible, minute details will be given concerning changes of title, sequence of series, editorship, and date of publication. The arrangement of titles will be strictly alphabetical, but periodicals having different names at different periods will be grouped together under the heading of the first or earliest title of the series, cross-references being made in all cases. A peculiar feature of the catalogue is presented in synoptical tables containing the dates of publication of each volume of the periodicals named, exhibited by a method slightly modified from the plan originated by Professor James D. Dana, and is described in his "System of Mineralogy" (page 34, foot-note). Only a limited number of the periodicals can be