84 THE NERVOUS SYSTEM 



one. The facts are comparatively simple; it is only how they are accom- 

 plished that physiology does not as yet explain. There are thousands 

 of unitary muscular bundles whose arithmetic combination would make 

 millions of possibilities of action. There are, too, thousands of pos- 

 sible outgoing nerve-paths whose possible combination would make other 

 millions of possibilities of action. All these millions combine in the 

 neuro-muscular mechanism, yet out of them normally the one right path 

 is chosen ! 



For the most part reflex actions are conducted without much influence 

 from the brain, especially from the cortex, but it appears certain that 

 impulses regularly do pass from the reflex spinal centers upward into 

 the brain. In general, it may be said that the cortex of the brain, during 

 waking hours at least, exerts a controlling influence over most of the 

 reflexes. Those movements are largely concerned with the purely vege- 

 tative processes, such as the movements of the alimentary canal and of 

 the heart. These have, however, become so nearly " automatic" that 

 in their normal condition they occur quite without the knowledge of 

 the individual, the nerve-impulses not being correlated with conscious- 

 ness. Still, it needs only some inflammation in these parts or disturb- 

 ance in their nervous mechanisms to show that, so far as the nervous 

 impulses are concerned, there is a very close constant relation between 

 even these organs and the cortex of the brain. 



The more highly developed the animal, the smaller the proportion 

 of his activity controlled by the spinal cord. In worms, for example, 

 there is no brain worthy to be called such, and the animal is wholly a 

 " spinal animal/' such as, for example, the frog becomes when its fore- 

 brain and mid -brain are destroyed. In future chapters we shall discuss 

 more in detail the relations of reflex actions to voluntary actions and to 

 mental function or consciousness. 



Although of many various sorts, the human spinal reflexes are not 

 very satisfactorily classifiable. We may think of them, however, as either 

 vegetative or non-vegetative, although every normal reflex has more or 

 less of a vegetative or basal value to the organism. For convenience, 

 however, we may arrange the spinal reflex-actions, including those of 

 the medulla, in these two classes. The former class, vegetative reflexions, 

 includes those which are essential to the life of the organism. Among 

 them are inspiration, expiration, sneezing, coughing, cardio-inhibition, 

 cardio-augmentation, vaso-dilation, vaso-constriction, thermogenesis y 

 thermolysis, sucking, mammillary erection, mastication, salivation, deglu- 

 tition, digestive secretion, digestive motion, vomiting, sweating, urination, 

 copulation, erection, ejaculation, parturition, winking, and pupillary 

 motion. The non-vegetative reflexes are very numerous if we include 

 many actions which merge indistinguishably into voluntary movements. 

 These are such actions as movements of self-defence, of withdrawal from 

 injury, walking, running, swimming, and speaking. Included in this 

 class are a number of skin-reflexes, the so-called superficial spinal re- 

 flexes: the gluteal, plantar, cremasteric, epigastric, abdominal, and 

 scapular reflexes. These are of much practical use to neurologists and 



