34 Master Minds of Modern Science 



prick your foot with a needle the message of pain has to 

 be flashed from the foot to the brain and back by means 

 of a chain of nerves. In a frog this interval is about one- 

 hundredth of a second, but in a plant it is fifty to seventy- 

 five times as long, and the interval is longer in cold 

 weather than in warm. It is also lengthened by fatigue. 

 In other words, if you try the same experiment several 

 times on the same plant the plant gets tired and the latent 

 period — as it is called — grows longer and longer. Sir 

 Jagadis considers that the line of cells along which the 

 impulse passes in a plant resembles the human nerves, and 

 that the plant begins to show traces of mind. 



There is a practical result from all this work, for Sir 

 Jagadis has discovered a large number of plants which 

 have medicinal properties, the existence of which had 

 never before been suspected. Some of these are especially 

 useful in cases of failing heart action. 



Sir Jagadis has done much more than enlarge our 

 knowledge of plants. He has worked on metals and dis- 

 covered that they too have the vital force. Metal- 

 workers have known for a long time past that metals can 

 suffer from fatigue. For that matter, every man who 

 owns razors knows that it is not good to use the same 

 blade day after day. A razor in daily use gets duller 

 and duller, even if stropped afresh at each time of using ; 

 but if it be laid aside for a few days it will recover its 

 keen edge. The X-ray has demonstrated that rest causes 

 the disturbed molecules to fall back into their original 

 positions. 



Sir Jagadis uses the galvanometer to test the fatigue of 

 metals. The galvanometer is a delicate instrument used 

 for detecting the presence of electric currents. It contains 

 a needle on a pivot, and this needle is deflected by even 

 the faintest of currents. Diagrams from galvanometer 

 tests show that metal resembles muscle in that its sensi- 

 tiveness grows less and less under repeated stimulation. 



