354 BIOLOGY. [Boox \r. 



not continue longer than the excitation itself which has provoked 

 it. This law is verified in the diverse apparatus of the verte- 

 brates ; it is verified still more visibly in invertebrates. Those 

 of them, for instance the mollusks, whose muscular system is 

 almost entirely composed of smooth fibres, move slowly. On 

 the other hand, the arthropods, which have a striated muscula- 

 ture, have movements vivacious, vigorous, and precise. 



Contractility is a property inherent in the muscular fibre, and 

 can be brought into play by diverse excitants. It exists in the 

 inferior invertebrates, and in the vertebrate d embryon when it 

 has not yet a nervous system. It persists in the superior and 

 adult vertebrate, when the nervous system has been killed by a 

 special poison. 



Like all the organic properties, contractility has nutrition for 

 necessary basis. It cannot be accomplished without influencing 

 the double assimilation and disassimilation movement indispen- 

 sable to the maintenance of the life of the muscular tissue. Every 

 contraction corresponds to a more energetic oxydation, to a more 

 active assimilation, to the formation and the elimination of dis- 

 assimilated products. The result is manifested immediately, in 

 the vertebrates, by changes in the colour, the composition and the 

 temperature of the blood which comes from the muscle, the 

 muscular venous blood. If a muscle is at rest, the venous blood 

 which comes from it is almost as rutilant as the fresh and oxy- 

 genised blood brought by the artery. The phenomenon is more 

 marked still in the case of paralysis, in certain maladies which 

 produce muscular atony, in syncope. The explanation is that the 

 muscle, in its state of rest, is at its minimum of consumption, 

 of life, of contraction ; it absorbs nothing more than is strictly 

 necessary to its maintenance. 



On the other hand, when the muscle contracts, it wears itself, 

 it expends itself ; it absorbs and eliminates more. Hence the 

 venous blood which comes forth from it becomes immediately 

 black. 1 



1 01. Bernard, Leyons sur Us Proprietes des Tissus Vivants, pp. 220-274. 



