THE STUDY OF MUSCLE PHYSIOLOGY. 203 



The muscles of the tortoise contract tardily but with great 

 power, resist fatigue weU, retain their vitality under unfavor- 

 able conditions, and after death for a very long period (days). 



Without resorting to elaborate experiments, the student may 

 convince himself of the truth of most of the above statements 

 by observing the movements of a water-snail attached to a glass 

 vessel ; the note made by the buzzing of an insect, and compar- 

 ing it with one approaching it in pitch sounded by some instru- 

 ment of music ; the force necessary to withdraw the foot or tail 

 of a tortoise ; the peristaltic movements of the intestine and 

 other organs in a freshly killed animal ; or the action of a bee, 

 wasp, or wood-boring beetle on the cork of a bottle in which 

 one of them may be inclosed. 



SPECIAL CONSIDERATIONS. 



In the case of weakly tuberculous animals a sharp tap on 

 the chest will often produce a contraction of the muscles thus 

 stimulated ; but, in addition, a local contraction lasting some 

 little time, known as a wheal or idio^muscular contraction, fol- 

 lows. This phenomenon seems to be the result of a special 

 irritability in such muscles. 



Cramp may arise under a great variety of circumstances, 

 but it seems to be in all cases either a complete prolonged teta- 

 nus, in which there is unusual muscular shortening in severe 

 cases, at least, or the persistence of a contraction remainder. 



The great differences known to exist between individuals of 

 the 'same species in strength, endurance, fleetness, and other 

 particulars in which the muscles are concerned, raise numer- 

 ous interesting inquiries. The build of the greyhound or race- 

 horse suggests in itself part of the explanation on mechanical 

 principles, lung capacity, etc. But when it is found that one 

 dog, horse, deer, or man excels another of the same race in 

 swiftness or endurance, and there is nothing in the form to 

 furnish a solution, we are prompted to ask whether the muscles 

 may not contract more energetically, experience a shortening 

 of the latent period or other phase of contraction ; or whether 

 they produce less of waste-products or get rid of them more 

 rapidly. The whole subject is extremely complicated, and we 

 may say here that there is some evidence to show that in races 

 of dogs and other animals which surpass their fellows the 

 nerve regulating the heart and lungs (vagus) has greater power; 



