CHAP, in.] ELECTRICITY AND MAGNETISM. 187 



tarily when the circuit is made or broken. A rapidly 

 interrupted current will induce a second contraction 

 before the first has had time to pass off, and the muscle 

 may exhibit thus a continuous contraction resembling 

 tetanus. The prepared frog after a short time becomes 

 less sensitive, and a " direct " current (that is to say, one 

 passing along the nerve in the direction from the brain 

 to the muscle) only produces an effect when circuit is 

 made, while an " inverse " current only produces an 

 effect when the circuit is broken. Matteucci, who 

 observed this, also discovered by experiments on living 

 animals that there is a distinction between the con- 

 ductivity of sensory and motor nerves, a "direct" 

 current affecting the motor nerves on making the 

 circuit, and the sensory nerves on breaking it ; while 

 an " inverse " current produced inverse results. Little 

 is, however, yet known of the conditions of con- 

 ductivity of the matter of the nerves ; they conduct 

 better than muscular tissue, cartilage, or bone ; but of 

 all substances in the body the blood conducts best. 

 Powerful currents doubtless electrolyse the blood to 

 some extent, coagulating it and the albumin it contains. 

 The power of contracting under the influence of the 

 current appears to be a distinguishing property of 

 protoplasm wherever it occurs. The amoeba, the 

 most structureless of organisms, suffers contractions. 

 Ritter discovered that the sensitive plant shuts up when 

 electrified, and Burdon Sanderson has shown that this 

 property extends to other vegetables, being exhibited by 

 the carnivorous plant, the Dionaea or Venus' Fly Trap. 



231. Animal Electricity. Although, in his later 

 writings at least, Galvani admitted that the electricity 

 thus operating arose from the metals employed, he 

 insisted on the existence of an animal electricity resident 

 in the muscular and nervous structures. He showed 

 that contractions could be produced without using any 

 metals at all by merely touching a nerve at two different 



