CHAP. I. OF THE ELEMENTARY ORGANS. 3 



ill-constructed glasses, is now generally abandoned. The 

 supposed pores, with their rim, have been ascertained to be, 

 in many cases, nothing but grains of semi-transparent matter 

 sticking to the membrane : this has been proved by Dutrochet, 

 who found that boiling them in hot nitric acid rendered them 

 opaque, and that dipping them in a solution of caustic potash 

 restored their transparency, — a property incompatible with a 

 perforation ; and any one furnished \nth a good modern 

 miscroscope may satisfy himself upon the point, without 

 going through Dutrochet's process; by simple movement in 

 water the grains may be often detached. In other cases 

 they may be thin spaces in the sides of tissue, such as might 

 be produced by the adhesion and separation at regular inter- 

 vals of a thread developed spirally witliin a membranous sac. 

 Such a view has been taken of them by Slack {Trails. 

 Soc. Arts, xlix.), as will be explained at page 16. A nearly 

 similar opinion was previously offered by Mohl, who considers 

 the dots on the membrane of tissue to be thinner portions of 

 it. He says it may be distinctly seen by the aid of a power- 

 ful microscope that the little round orbs which are visible in 

 the surface of membranes in the tissue of Palm-trees are pas- 

 sages (meatus) in the thickness of the membrane, opening 

 into the cavity of the cells, and closed externally by the mem- 

 brane itself He adds, that when dotted tissue is in contact, 

 these passages are placed exactly opposite to each other. {Mar- 

 tins Palm. Anat. v. col. 2.) In matters demanding such very 

 delicate observation as this, it is excessively difficult to know 

 what dependence can be placed upon the statements and di^aw- 

 ings of even the most skilful anatomists. We must therefore 

 wait for further e\adence of these supposed facts before they 

 can be received into the certain truths of science. It, however, 

 occasionally happens that holes do exist in the membrane, of 

 which mention will be made hereafter. 



Elementari/ Fibre may be compared to hair of inconceivable 

 fineness, its diameter often not exceeding the ts^jtt of an inch. 

 It has frequently a greenish col om', but is more commonly trans- 

 parent and colourless. It appears to be sometimes capable 

 of extension with the same rapidity as the membrane among 



B 2 



