EIGHT FIGURES
Tlie " spontaneous " activity iii the ceriti*al iicwous system of' tlic ci.ayfisli pi.ovides a hactkgi*ound upon which all responses to sciisoi*y stiiiiulatioii must be studied. The dependence of tliis "spontaiieous" activity upon the ratio of the potassium iiisicle to that outside the neui.ones lias been shown by Prosser ( '39). The present paper is a n attempt to ascertain first, whether any liumoral agents such as are postulated in some vertebrate centers play a role in tlie "spontaneous" activity; second, whether these humoral agents take part in synaptic transmission iii the crayfish, and third, to investigate otlier possible niechanisiits of synaptic transmission.
,410ng the margin of the tail lobcs of tlie crayfish a r e sensory hairs ; stimulation of these sets up impulses iii sensory fibers going to the sixth abdoiiiiiial ganglion. Rapid flexion of one sensory hair gives rise to one afferent impulse. The number of afferent impulses recorded from one cauclal nerve can be controlled by varying the number of hairs stimulated. The afferent bursts are relayed in the sixth abdominal ganglion to neurones passing anteriorly in the ventral nerve cord. By recording * I am grateful to Ur. John I,. Fuller for assistance in 80111~ of tlic early exlxxiinents of tlw