186 GENERAL PROPERTIES OF LIVING TISSUES 



electrometer. Similar measurements can be 

 made with a differential rheotome (page 313). 



Helmholtz found in motor nerves of the frog 

 an average speed of 27 metres per second, but 

 the individual variation is considerable. The 

 speed is very slow compared with that of light, or 

 even sound. It is modified by changes in tem- 

 perature, nutrition, anaesthetics (alcohol, ether, 

 chloroform, carbon dioxide), the intensity of the 

 stimulus, above a certain value, the greater 

 the stimulus, the more rapid the conduction, 

 and by many other factors. Specific differences 

 are found depending on the structure of the 

 nerve. Thus the velocity has been found in mam- 

 malian nerve to smooth muscle to be about 9 

 metres per second, while in the bivalve Anodonta 

 it is said to be only 1 centimetre per second. 



APPARATUS 



Normal saline. Bowl. Towel. Pipette. Glass plate. 

 Dry cell. Inductorium. Key. Wires. Frog with sci- 

 atic nerve degenerated. Hen's egg incubated 60-70 hours. 

 NaCl solution (0.75%). Ligatures. Filter paper. One 

 per cent solution of curare. Pole-changer. G-as chamber. 

 Carbon dioxide generator. Twenty per cent hydrochloric 

 acid. Broken marble. Alcohol. Muscle clamp. Stand. 

 Muscle lever with scale pan. Millimetre rule. Ten gram 

 weights. Needle electrodes (glass tube). Moist chamber. 

 Two pairs of non-polarizable electrodes. Electro-magnetic 

 signal. Recording drum. Glazed paper. Tuning fork. 

 Normal saline clay. 



