OF THE HUMAN SKm. 65 



scarcely crushed between the glass slides of the 

 microscrope. Before they are thrown off they are 

 not so firm, but more elastic and pliant. They do 

 not lose their power of germinating by drying, 

 except under a heat of 150" Fahrenheit. Being 

 less dense than water, they float upon it, and are 

 by that means also spread far and wide. They 

 are nearly colorless — gray, brown, or yellowish 

 when possessing any color. When in numbers, 

 they give a gritty feel, and mouldy taste and 

 smell. They are not much affected by chemical 

 agents. Tincture of iodine gives them a dark, 

 yellowish-brown look, like other purely nitrogen- 

 ous substances. When their cellulose walls are 

 not colored blue by the action of the iodine, their 

 nitrogenous contents become brown. On treating 

 them with hydrochloric or nitric acid, or hot sul- 

 phuric acid, before adding tincture of iodine, the 

 nitrogenous part coagulates, contracts, separates 

 from the sides of the spores, and remains, forming 

 irregular masses in the centre. On applying, 

 afterwards, tincture of iodine to these parts, they 

 become brown, and the cellulose walls greenish 

 — the complementary color of the blue of the 

 cellulose and the brown of the tincture of iodine. 



6 



