LESSON 12.] SILICA. 37 



Earth's surface, that the temptation to figure and describe them is 

 very great ; belonging to the vegetable kingdom, too, such a proceed- 

 ing would be quite justifiable in this place but it would transcend the 

 limits of the present work. 



220. The grasses, which include all the Cereal grains, Canes, 

 Horse-tails, &c., are conspicuous for the large amount of silica which 

 enters into their composition. Who has not marvelled at the singu- 

 larly erect position of a stalk of wheat, or rye, or barley, each support- 

 ing a heavy ear of grain at its summit ? 



221. And yet how few persons have enquired how it is, and why, 

 that a slender stalk can grow so tall, and maintain, even against ad- 

 verse elements, its perpendicular, erect form. 



222. If a piece of straw of wheat, or any other cereal, be boiled 

 in strong nitric acid, well washed in clean water, and examined by 

 the Microscope, the secret will be developed ; it will then be seen that 

 it is defended from the root to the summit with a coat of pure, beau- 

 tifully transparent silica, composed of millions of minute particles, 

 all nicely jointed or fitted to each other. 



223. Upon this principle all the grasses are defended by a skele- 

 ton (as it were) composed of flint. The silica of the husk (chaff) of 

 the rye, is shown at Fig. 65 ; it consists of a number of long bars 



Fio 65 (6), connected with smaller oval bodies (a) 



these are the casts in flint of the stomata, or 

 breathing mouths. 



224. The husks of all the cereals, together 

 with the hairs (palese), are also entirely cov- 

 ered with flinty matter, and those persons who 

 indulge to much extent in the use of oat-cake, 

 or brown bread, are liable to large concretions 

 of flinty matter (that no stomach can possibly 

 digest) forming in the intestinal canal, which 

 must necessarily (sooner or later) prove fatal. 



225. In the Museum of the Royal College 



of Surgeons, England, several such masses may be seen, all the result 

 of post-mortem examinations. 



226. The Microscope has satisfactorily determined, long ago, that 

 some of these concreted masses are composed of silica of the oat, and 

 others of the silica of wheat, obtained from the intestines of the in- 

 veterate eaters of brown bread, or oat-cake. 



227. There is a popular prejudice in favor of this description of 

 food, and used occasionally, and in moderation, it is well founded. 



