ZOOLOGY. 349 



ent stages of growth, having both valves studded with pearls, has fully dem- 

 onstrated its truth. A tinge of yellow is found over the whole inner surface 

 of some shells, showing that the more recent secretion of nacre by the suffer- 

 ing animals was unnatural ; the flesh of all, however, is eaten. 



Above five thousand families are represented as being engaged in this sin- 

 gular branch of industry in the villages of Chungkwan and Sian-chang-ngan ; 

 they, however, mainly derive their support from cultivating the mulberry, and 

 in rearing silk- worms, and other agricultural occupations. Those who are not 

 expert in the management of the shells lose 10 or 15 per cent, by deaths; 

 others lose none in a whole season. 



NEW THEORY RESPECTING THE CHOLERA. 



A work of considerable importance has been published in Germany during 

 the past year by Dr. Max Pettenkobey, bearing the title: " Investigations 

 and Observations in regard to the Propagation of Cholera, with Reflections on 

 the proper means of arresting its Progress." The author is Professor of Medic- 

 inal Chemistry at the University of Munich, and has been employed by the 

 government during the whole of last year investigating the progress and 

 mode of propagation of the disease in the principal towns of Bavaria, The 

 present work is the result of his and other physicians' researches, in the form 

 of a report to the government, and has given such complete satisfaction that 

 its gratuitous distribution has been ordered throughout the kingdom at the 

 expense of the government. 



The author advances no new theory, but produces a volume of facts of a 

 most positive and conclusive character. These facts could hardly have been 

 ascertained with the same precision in any other country ; for not only would 

 it have been impossible to ascertain age, condition, mode of life, etc., of the 

 sick, but the patients themselves would not willingly have subjected them- 

 selves to a similar control. Observations were made in Munich, Nuremburg, 

 Augsburg, "Wurzburg, Ebrach, Ingolstadt, Gairnersheim, Rattisbone, Fraun- 

 stein, and Freysing, and the author compares Ms results with the " Report of 

 the Mortality of Cholera in England, 1848-49," and the reports on the cholera 

 in India, during the years 1817, 1818 and 1819, by James Jameson. He 

 shows conclusively that there is no contradiction in these reports that the 

 facts ascertained in India are precisely those which have been observed later 

 in England, and but last year in Bavaria ; that any apparent contradiction is 

 due solely to accompanying circumstances by which the results were modified, 

 and which in part are mentioned by the authors themselves. The facts which 

 Dr. Pettenkober claims to have fully established are as follows : 



1. That it is not contagious, in the usual sense of the word ; but that it 

 can. nevertheless, be carried from one place to another. 



2. That it always follows the usual routes of commerce. 



3. That no elevation above the level of the ocean, furnishes a guaranty 

 against the disease nor is any depth necessarily exposed to its ravages. 



4. That no contagious cholera matter is floating in the atmosphere, and 

 that consequently the disease is not propagated by currents of air. 



