538 THE STINGING PROPERTY OF THE GIANT NETTLE-TREK, 



The hairs are seen to be hollow tubes with circular section, 

 and contain a strong acid. Some are only partly filled and show 

 a distinct meniscus, while others are completely filled to the tip. 

 By carefully watching the action of litmus solution on suitable 

 sections under the microscope the glandular tissue of the basal 

 cushion is found to be strongly acid only round the bulb of the 

 hair, and in the rest of the cushion cells the litmus remains blue 

 for some time. The blue litmus is also observed to quickly 

 become red in the cells of the epidermis. 



The root-bulbs of the hairs are also filled with the strong acid, 

 and when gently pressed air bubbles form which move about in 

 the interior. Empty hairs can be filled completely by pressing 

 the root-bulbs and tiny drops of acid made to ooze out from the 

 open ends. 



To ascertain the composition of the hairs, some of them were 

 shaved off and heated to redness on platinum. Microscopic 

 examination then showed that they were considerably cracked 

 and broken, yet otherwise unaltered in structure. These burnt 

 hairs were next submitted to the action of boiling strong hydro- 

 chloric, nitric and sulphuric acids, and from this ordeal they 

 came out practically unchanged. 



The hairs are therefore hollow siliceous tubes, which when 

 fresh seem to be glassy silica, and after heating naturally appear 

 opaque and white. On the other hand, the hairs of the common 

 nettle are always described as having their walls silicified at the 

 end only, and calcified for the rest of the length (1). 



Physiological Action. — The sting is undoubtedly due to the 

 free acid existing in a concentrated form in the hairs, and differs 

 from the sting of the common nettle only in degree. 



Common nettle plant contains 0002% formic acid. 



Giant nettle-tree contains 0-179 % (0-002 % formic and 0-177 % 

 acetic). 



That is, Laportea gigas contains 90 times more free acid than 

 Urtica urens. 



The amount of strong acid injected under the skin by one of 

 the large hairs is quite a sufficient cause for the severe shock 



