132 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



to irregular contractions of the separate fibres, the combined action of which 

 produces more or less regular continued contraction. Another view would be 

 that contracture might be produced under the influence of the changes caused 

 by the electric current, and a condition result similar to that which causes 

 the prolonged contractions characteristic of poisoning with veratria, etc. 



Effect of Death Processes. — If a muscle be dying, it responds to excitations 

 by very slow, weak, and prolonged contractions, definitely localized at the 

 place excited. Such a form of contraction is often classed as contracture, in 

 spite of the fact that the irritability is greatly lessened. This form of con- 

 traction may be seen toward the end of prolonged wasting diseases in the case 

 of the muscles of men. They respond to mechanical stimulations by local- 

 ized, slowly developing contractions. 



Pathological Contracture of Central Nervous Origin. — In certain patholog- 

 ical conditions there may be contractures which do not depend upon the con- 

 dition of the muscle, but which originate in the central nervous system. In 

 these eases the muscles are in continuous receipt of nerve impulses from the 

 spinal cord cells, and are kept in continuous contraction, which varies in degree 

 from the amount observed during ordinary reflex muscle tonus to a state of 

 intense rigidity. The peculiarity of the condition is its endurance. The 

 muscle does not appear to fatigue ; moreover, it is said that it does not 

 develop the large amount of heat (Brissand et Regnard) which is always 

 formed as a result of the chemical changes which take place during the ordi- 

 nary contractions. 



For these reasons, Richet ' considers the shortening of the muscle to be 

 not a true contraction, but the result of an increase of elasticity. It is possi- 

 ble that some pathological contractions may be of different nature from those 

 which we have been considering, but they have not been studied sufficiently 

 to enable us to draw definite conclusions from them. 



(d) Norma/ Physiological Contraction*. — All normal physiological con- 

 tractions of muscles are regarded as tetani. Even the shortest possible vol- 

 untary or reflex movements are considered to be too long to be single contrac- 

 tions. Inasmuch a> we can artificially excite normal muscles to continuous 

 contraction only by means of a series of rapidly following stimuli, we find it 

 hard to explain continuous physiological contractions on any other basis, and 

 hence the view that the excitation sent by the nerve-cells to muscles has 

 always a rhythmic character, and that the normal motor-nerve impulse is a 

 discontinuous rather than continuous form of excitation. The view is prob- 

 ably correct, but cannot be considered as proved. The evidence in favor of 

 it is as follows : 



Muscle-sounds, Tremors, etc. — During voluntary muscular contractions the 

 muscle gives out a sound, which would imply that its finest particles are not 

 in a state of equilibrium, but vibrating. By delicate mechanisms it has been 

 possible to obtain records of voluntary and reflex contractions which showed 

 oscillations, although the contraction of the muscle appeared to the eye to be 

 1 Dictionnaire de Physiologie, 1899, iv. p. 393. 



