POPULAR MISCELLANY. 



421 



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 extreme- 

 ly disastrous explosion of nitro-glycerine 

 took place in San Francisco in 1880, a vio- 

 lent concussion was felt in the University 

 buildings, three miles away, while no aerial 

 shock was felt at Professor Joseph Le 

 Conte's house, eight hundred and ninety feet 

 farther off, but within the geometrical shad- 

 ow of one of the buildings. The sound-wave 

 coming by the air was completely cut off 

 by the acoustical shadow cast by the inter- 

 vening: 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 So- 

 ciety on the disease which prevails occasion- 

 ally among the salmon in North America 

 and Siberia, in which he reviewed the re- 

 sults of the commission that was appointed 

 in 1878, when the disease raged in the Sol- 

 way district, to investigate its nature. The 

 evidence taken before the commissioners 

 leaves no doubt that the malady is to be as- 

 signed to the diseases caused by parasitic 

 organisms, and that it is a contagious and in- 

 fectious disease of the same order as ring- 

 worm, 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 liv- 

 ing plants for their support, while the Sa- 

 prolegnia 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 zoospores of these 

 plants, diffused through the water, germi- 

 nate and produce a mycelium similar to that 

 from which they started as soon as they 

 reach the healthy skin of a salmon. Pro- 

 fessor Huxley experimented in inoculating 

 the bodies of dead house-flies from the dis- 

 eased salmon-skin, and in a few hours saw 

 the bodies completely ttrken possession of 

 by the white filaments of the fungus ; it 



was proved to him that the pathogenic Sa- 

 prolegnia 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 in- 

 sects infested with the Sapn-olegnia 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 ab- 

 sent," although they may favor the condi- 

 tions on which its spread depends. Profess- 

 or 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 extir- 

 pation 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 pre- 

 paring for the press his long-delayed " Cata- 

 logue of Scientific Periodicals," which will 

 appear in the octavo series of the Smith- 

 sonian Institution. The catalogue is intend- 

 ed to embrace independent journals of pure 

 and applied science, published in all coun- 

 tries, from 1665 to 1880 ; so far as possible, 

 minute details will be given concerning 

 changes of title, sequence of series, editor- 

 ship, and date of publication. The arrange- 

 ment 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 ta- 

 bles containing the dates of publication of 

 each volume of the periodicals named, ex- 

 hibited 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 en- 



