SCIENCE OF COMMON THINGS. 311 



Preservation of wood. Miasm. Contagion. 



SOO6 Are loth these compounds, calomel and corrosive sublimate. 



poisons f 



They are / corrosive sublimate, especially, is a most 

 deadly poison. In case of poisoning by it, the most 

 effectual antidote is white of eggs. 



SOOT* What is the process of preserving wood from decay, commonly 

 termed " kyanizing ? " 



It consists in saturating the fibres of the wood with 

 a solution of corrosive sublimate. 



Poisonous substances, and corrosive sublimate especially, have the pro 

 perty of protecting animal and vegetable substances from decay. The 

 skins of stuffed birds and animals, and the plants of a herbarium, may be 

 protected from insects and decay, by washing them with a solution of cor- 

 rosive sublimate. It should not, however, be forgotten, that these sub- 

 stances by such treatment become themselves poisonous. 



SOOS What is contagion ? 



We apply the term contagion to that subtle matter 

 which proceeds from a diseased person or body, and 

 which communicates the disease to another person or 

 body. 



Contagion differs from miasm in being the product of disease, arid in 

 reproducing itself. 



J2OO9 What is miasm or miasmata ? 



Miasm or miasmata is the product of the decay or 

 putrefaction of animal or vegetable substances, and 

 causes disease without being itself reproduced. 



Contagion occasions disease in the same way that yeast excites fermen- 

 tation. Miasm often acts, by its chemical properties merely, as a poison. 



SO1O Why are contagious diseases sometimes communicated to indi- 

 viduals who merely approach the vicinity of diseased persons, but do not come 

 in contact with or even see them ? 



Because the air itself, which has been in contact with 

 the diseased persons, carries with it the seeds or germs 

 of infection, and thus communicates disease, sometimes 

 at great distances. 



SOU Why are not all persons affected alike when exposed to similar 

 contagious diseases ? 



Contagious matter is not capable of producing dis- 

 ease, unless a compound is present in the system capable 

 of being decomposed ly contact with the exciting body. 



