AUTOMATIC ACTION. 627 



lated by a centre in the medulla, nearly related to the cardiac 

 centre that every vascular region has a nervous mechanism of 

 its own in the cord, which suffices to keep up the tonic contraction 

 of the muscular coat of its vessels as soon as the necessary new 

 lines of intercommunication have been opened between the differ- 

 ent districts most nearly related to it. 



2. Sweating centres : Though closely related to the preced- 

 ing, the centres which preside over the secretion of sweat in the 

 lower part of the body and hinder extremities must, for many 

 reasons which cannot now be mentioned, be regarded as separate 

 centres. 



3. Many sets of smooth muscle-fibres appear to be kept in a 

 state of tonic (automatic) contraction by means of centres in the 

 cord. Thus, in the lower part of the cervical cord is a group of 

 nerve-cells which keep the dilator muscle of the iris partially con- 

 tracted ; a narrowing of the pupil has been described as following 

 injury of this region. 



4. The gray matter of the cord is also said to keep the skeletal 

 muscles in a state of slight tonic contraction, either from auto- 

 matic or reflex stimulation. 



On account of the elaborate and purposeful reflex movements 

 performed by decapitated frogs or eels, it has been suggested 

 that in the lower vertebrates the spinal cord is capable of sensation 

 and volition mental activity but to follow this assumption, we 

 should have to modify our ideas of volition and sensation, for 

 which consciousness is commonly taken to be a necessary factor. 

 It is, however, important to note that the lower we come in the 

 scale of vertebrate animals the less powerful are the mental facul- 

 ties, and the more important are the functions that the spinal 

 marrow presides over. 



