The experiments of physiologists have shown that if a sensory irritation of a given spinal nucleus be kept up, after having produced a reflex movement in the same segment, any reaction beyond the plain of that segment is not in the next or succeeding planes but in the medulla oblongata. The motor reaction then manifests itself in laughing, crying, or deglutitory spasms, and, if the irritation be of the severest kind, epileptic or tetanic spasms in addition. Now the occurrence of laughing, crying, or deglutitory spasms could be easily understood if the molecular oscillation induced by the irritation were to travel along the associating tracts from the given spinal segment to the nuclei of the medulla oblongata. For in the medulla are found the nerve nuclei which preside over the facial, laryngeal and pharyngeal muscles. It is not easy at first to understand how tetanus and epilepsy, that is, spasms consisting in movements whose direct projection is not in the medulla oblongata but in the cord, can be produced by irritation of the former. There are scattered groups of nerve cells in the medulla oblongata which have either no demonstrable connection with the nerve nuclei, or are positively known to be connected with the longitudinal associating strands. These cells hence can safely be regarded as representing a presiding centre over the entire spinal system. No spinal centre exerts any influence even remotely as pronounced as that of the entire cord. This applies to man and other mammals. That the elaboration of the medullary centre was as gradual a process as that of other higher differentiations is illustrated by the case of the frog, whose medulla has acquired the faculty of reproducing general spasms while the spinal cord itself retains this property also; hence here the predominance of the medulla is not so marked as in mammals. The reticular ganglion of the oblongata is not in the adult a part of the central tubular grey matter, but has, through originally developing from it in the embryo, become ultimately isolated from its mother bed. It constitutes a second ganglionic category, and the association fibres bringing it in functional union with the spinal grey (first category) in lower animals and shown to have assumed the position of projection fibres in the higher, constitute a second projection tract; both together are a second projection system. The scattered grey matter of the medulla has great importance. Anatomically it is (though its cells be scattered diffusely as a rule) a large ganglion with numerous multipolar cells of all sizes, many of them gigantic, sometimes exceeding the so-called motor cells (which they simulate in shape) of the lumbar enlargement in size. Scattered in the "reticular substance" of the medulla from the upper end of the fourth ventricle to the pyramidal decussation, they merit the collective designation of reticular ganglia.