ORUSHING INSTRUMENTS- 321 



and by druggists for similar purposes. In these instruments 

 the point of the knife is jointed to some fixed object, and 

 becomes the fulcrum ; the hand of the cutter supplies the power, 

 and the weight is the object which is being cut. It will be 

 seen that, by increasing the length of the handle, very great 

 power can be obtained. 



Exchanging the power for weight, we have in the common 

 tongs, whether used for the coals or for sugar, a leverage of a 

 similar character, the weight moving over a greater space than 

 the power. A good example of this is to be found in the 

 deltoid muscle of the human arm. The muscle, which furnishes 

 the power, contracts about an inch, and, so doing, moves the 



JAWS OF WOLF-FISH. NUT-CRACK&RS. 



hand over some forty inches of space. It has been well stated 

 that if a man is able to hold in his hand, and with extended 

 arm, a weight of twenty-five pounds, the muscle must be exert- 

 ing a power of forty times as great, i.e. about a thousand 

 pounds. 



There is little doubt that, in such Crushing Instruments as 

 have been mentioned, the idea has been taken from the jaws of 

 sundry animals. We know, for example, that with ourselves, 

 if we desire to crack a walnut or a filbert in our teeth, we 

 always put it as far back as possible, so as to make the leverage 

 as powerful as possible. No one would ever dream of crack- 

 ing a nut with his front teeth, an act which would be very 



