102 ELECTRO-PHYSIOLOGY 



as described above. If any considerable tonus has been induced 

 by the mechanical stimulation consequent on removal of the 

 mucosa, it only yields very gradually at normal temperature. 

 On the other hand, the lever drops with increasing rapidity if the 

 temperature is raised about 25 40 C. If the muscle is 

 tetanised during this period, the contractions obtained are much 

 more vigorous, which is due less to increase of excitability than to 

 diminution of tonus. Extension ceases between 45 and 50 C., 

 simultaneously with excitability, and contraction first reappears 

 at about 57 C., being then produced in great measure by rigor. 

 Here we have the same fact as that demonstrated by Gad and 

 Heymans in striated muscle, i.e. that excitability to electrical 

 stimuli disappears almost entirely before contraction occurs from 

 heat rigor. Previous to this, every cooling of the preparation 

 had produced a contraction, i.e. a reinforcement or restoration of 

 tonus. Griinhagen and Samkowy confirmed the same reaction in 

 the bladder muscles of the frog, while, on the other hand, many 

 smooth muscles or warm-blooded animals (sphincter iridis, muscles 

 of oesophagus) exhibit the contrary under similar conditions, con- 

 tracting with warmth, and relaxing when cooled again. It must, 

 however, be remembered that the effects of warming or cooling 

 are essentially conditioned by the temporary state of the excitable 

 substance, i.e. in the case above, by the degree of tonus. This 

 again depends undoubtedly upon the conservation of normal vital 

 conditions, in particular of normal temperature. It is therefore 

 quite conceivable that the smooth muscles of warm - blooded 

 animals may sometimes be atonic, when the corresponding 

 elements of cold - blooded animals exhibited a marked tonus. 

 This may account partially at any rate for the contradiction, in 

 the above authors, as to the behaviour of smooth muscle in warm 

 or cold-blooded animals. It is certain that in living animals, the 

 smooth muscle of the blood-vessels relaxes locally when sufficiently 

 warmed (application of a heated body to small exposed artery), 

 and responds under these conditions like the elements of cold- 

 blooded animals. Horvath (65) observed that the tracheae of 

 mammals widened on heating (relaxation of muscles), but became 

 narrow on cooling (contraction of smooth elements). 



Striated cardiac muscle also falls, under some conditions, into 

 a state of permanent (tonic) contraction, and then presents a very 

 favourable subject for the study of action of temperature upon 



