92 OYSTERS, AND ALL ABOUT THEM. 



small polygonal prisms, and is somewhat friable. Each of 

 these substances, the nacreous and the prismatic, consists 

 of layers of organic matter impregnated with salts of 

 lime." (c) 



Even now we have not exhausted the wonders of the 

 oyster's shell ; for its two valves are not loose, like the 

 plate that holds the bachelor's solitary muffin and the one 

 that is placed upon it to preserve its warmth ; nor are 

 they like the paper covers of a book, either of which gives 

 way on a slight wrench. On the contrary, they are united 

 at the back by a hinge-joint, artificially constructed, 

 and secured by a substance of great strength. 



According to the oyster's ordinary state, its abode is 

 kept open for a little distance, so as to allow the ingress 

 and egress of the water indispensable for respiration and 

 nourishment ; (d} but as a security against danger, the 

 in-dweller is able to close its shell, and firmly to hold its 

 valves together. Of this power many an opener of oysters 

 has had full evidence ; for there is no little difficulty in 



(c) Professor T. H. Huxley. A Lecture delivered at the Royal 

 ^^H Institution, Friday, May n, 1889. 



(d) Relative to the tiny organisms only visible under the micros- 

 cope, and called by scientists " infusoria," the following items may 

 prove interesting to the reader : By way of experiment, some of the 

 infusoria, along with some fragments of putrid fungi, were violently 

 boiled for several minutes, and immediately afterwards sealed up. As 

 long as they remained sealed up, no signs of life were visible ; but 

 when, after several months, the flask containing them was opened, the 

 infusoria almost immediately showed signs of returning animation, and 

 in a few hours were as full of life as if they had never been boiled. It 

 has also been demonstrated that they are equally well able to bear 

 cold, for in a decoction containing some of them, after being frozen 

 solid for a week, it was found, on thawing, that the infusoria were as 

 lusty and active as ever. 



