234 NATURE'S TEACHINGS. 



plate occupies the centre of the blade, and the soft iron is on 

 either side. Thus the thin plate of steel is easily brought to an 

 edge, while the soft iron can be ground away without any diffi- 

 culty. 



I do not mean to state that the inventor of this combination 

 of thin steel and soft iron had taken his idea from the Rodent 

 tooth, but only to show that the invention, beautiful, simple, 

 and ingenious as it is, has its prototype in Nature. I may 

 here mention that the Plane-iron, which is, in fact, a modified 

 Chisel, is made in exactly the same fashion. 



NEXT we come to the Adze. 



In some respects there is much resemblance between the 

 blade of the Adze and the teeth of the Rodent, especially in 

 their curve, which is almost identical in both. This form is 



ADZB-TEETH OP HIPPOPOTAMUS. STONE ADZE OF POLYNESIA. 



STEEL ADZE. 



seen in the structure of other teeth than those of Rodents. 

 There is, for example, the tooth of the Hippopotamus, which is 

 not only curved, like that of the Rodent, but bevelled off in a 

 similar way at the tip. With these formidable teeth, one of 

 which is now before me, the Hippopotamus makes terrible 

 havoc among the herbage, mowing it down, so to speak, and 

 stowing it away wholesale in its enormous stomach. A Hippo- 

 potamus indeed, when angered, has been known to sever a 

 man's body completely in two with a single bite, so trenchant 

 are the teeth, and so powerful the jaws. 



Then there is a little animal called the Hyrax, or Rock- 

 rabbit, which is the coney of Scripture. This creature is really 

 one of the pachydermatous group, although its small size, hairy 

 coat, its activity among the rocks, and its apparently rodent 



