104 SCIENCE FROM AN EASY CHAIR 



Fig. i 5 bis). It is, in fact, a living " cell," or life unit 

 The space in the cell not occupied by protoplasm is filled 

 with clear liquid, which contains the poison. This has 

 been examined chemically by using a large quantity of 

 ntttle hairs, and is found to contain formic acid the same 

 irritating acid which is secreted by ants when they sting, 

 whence its name. But later observations show that the 

 juice of the nettle hair contains also a special poison in 

 minute quantities, an albuminous substance, which resem- 

 bles that contained in the poison-sacs at the base of the 

 teeth of snakes. 



In tropical regions there are nettles far more power- 

 ful than that of our own country. The one called 

 Urtica stimulans, which is found in Java, and that called 

 Laportea crenulata, found in Hindostan, when bruised 

 emit an effluvium which poisonously affects the eyes and 

 mouth, and if handled produce convulsions and serious 

 swelling and pain in the arms, which may last for three 

 or four weeks, and in some cases cause death. They 

 are not unknown in the hothouses of our botanical 

 gardens, and young gardeners are sometimes badly 

 stung by them. There are other plants provided with 

 poisonous stinging hairs besides the true nettles or 

 UrticacecB) though they are not numerous. The Ameri- 

 can plants called Loasa sting badly, so do some of the 

 Spurges (Euphorbiacece), and some Hydrophyllece. 



The Chinese primrose (Primula obconica), lately intro- 

 duced into greenhouses, has been found to be almost as 

 injurious as the poison-vine. Its effects, of course, are 

 limited to a much smaller group of sufferers. And it is 

 worth while, in connection with poisoning by primula and 

 the poisoning by Rhus toxicodendron of only certain in- 

 dividuals predisposed to its influence, to point out that the 

 malady known as hay fever seems to be similar in its 

 character to these vegetable poisonings. It is, of course, 



