OF ARTS AND SCIENCES. 



35 



is one cause of the stains and some other injuries often seen in 

 stones used for building purposes. He mentioned several 

 buildings which had thus been disfigured, and remarked that 

 the Washington Monument would, in course of time, be de- 

 faced from this cause. 



The leprosy is described as being " in the walls of the house, 

 with hollow streaks, greenish or reddish, which in sight are 

 lower than the wall." And the remedy is given, — the re- 

 moval, of the affected stones, their replacement by others, and 

 the scraping and plastering of the house. 



He thought that the " leprosy of the house " alluded to, 

 was caused by the decomposition of this salt of iron ; the 

 greenish color being due to the presence of the sulphate, and 

 the reddish to the peroxide of iron. The limestone used for 

 building in that locality he had found to contain iron pyrites. 



He also alluded to a leprosy in clothing, arising from a 

 spontaneous change in the improperly cleansed wool from 

 which they were made. 



Dr. Bigelow, after alluding to a supposed connection be- 

 tween leprosy and this change in the walls of a house, ob- 

 served that the cause of epidemics is completely unknown, 

 and that the reference of them, to specific causes has always 

 been in proportion to the ignorance of the people. 



Professor Jeffries Wyman made a verbal communication on 

 the effects of physical agents on the development of life. He 

 had repeated some of the experiments of Milne-Edwards on 

 the influence of a low temperature and the absence of light 

 on the development of frogs. 



The tadpoles experimented upon were those of the common 

 bull-frog (Rana pipiens, Lin?i.). These, under ordinary cir- 

 cumstances, are hatched in the spring, and acquire their full 

 growth during the autumn, when a few midergo their meta- 

 morphosis ; but in the larger number, this does not take 

 place till the following spring, the tadpole period lasting about 

 one year. 



On the 8th of November, 1851, about thirty tadpoles con- 



