38 VEGETABLE PHYSIOLOGY. [LESSON 13. 



There can be no doubt that the minute particles of flint, liberated by 

 the digestion of the food, will have a tendency to slightly irritate the 

 mucous membrane of the stomach and bowels, thereby increasing the 

 circulation of the blood, and waking up (as it were) the dormant en- 

 ergies of the muscular coat of these tissues. But this increased ac- 

 tivity is intended to expel or digest the foreign enemy, the flint, and 

 when repeated attempts of this kind end only in failure, the stomach 

 and intestinal canal relapse into a state of increased torpor, and leave 

 the obnoxious substance to pass, or not, as it may ; these are the cir- 

 cumstances which originate concretions. 



228. In the Kingdom of Saxony there is a mountain range 

 of many miles extent, composed of a white, pulverulent earth, 

 called by the inhabitants Berg-mehl, Mountain-meal. In seasons of 

 scarcity, the people are wont to mix this Berg-mehl with equal parts 

 of flour to make their bread, and assert that it is not unwholesome. 

 During a short period in the Summer months, this practice is found 

 in most seasons to prevail, without bad results. 



229. Examined by the Microscope, the Mountain-meal is found 

 to consist principally of a number of minute fossil diatoms, but chiefly 

 of a form limited (almost) to this formation Campilodiscus clupeus 

 (Fig. 66). All that remains of this fossil is the flinty lorica (shell), 

 with its minute, sharp processes, which are likely to occasion the 

 same amount of irritation as that resulting from the flint of the 

 wheat, or oat. 



LESSON XIII. 



SILICA (CONCLUDED). 



230. The silicious particles of the Oat (Fig. 67) resemble those 

 of the Rye, except that they are smaller in size ; in the Wheat (Fig. 

 68) they are not smaller; the same elements will be found in all these 

 illustrations, that is to say, the lengthened bar and the connecting 

 rounded piece a cast in flint of the breathing mouth. Moreover, 

 the bars have all serrated (toothed, like a saw) edges, by means of 

 which they lock into each other to form a continuous tissue, just as 

 the bones of the human skull interlock at the sutures. 



231. The flint obtained from the husk of the Rice, differs some- 

 what from the preceding illustrations (Fig. 69). Here we find that 

 the bars are shorter and broader, the serratures finer and more uni- 



