710 PHYSIOLOGY. 



Ether and pilocarpin increase flow of cerebro-spinal fluid, whilst 

 atropine slows it, and amyl nitrite has no particular effect. Medi- 

 cines, as a rule, and the toxins of bacteria, do not appear in the 

 cerebro-spinal fluid when given by the mouth or subcutaneously. 

 Strychnia injected into the cerebro-spinal fluid has a very intense 

 action, as much as when ten times that quantity is injected into the 

 blood. Cocaine injected into the cerebro-spinal fluid causes an anaes- 

 thesia in the lower extremities, lasting forty-five minutes. Whilst 

 chemical substances with difficulty appear in the lymph when in- 

 jected into the blood, they appear quite readily in the blood when 

 injected into the lymph-tracts. 



REACTION-TIME. 



When a terminal organ of special sense is irritated, the time 

 between this stimulation and the moment when motion ensues as the 

 result of conscious perception of the irritation is called reaction-time. 

 Miiller's law of specific energy of sensory nerves is that irritation of 

 nerves of special sense always causes sensations of the same kind. 

 Thus, when the nerve of hearing is irritated by different agents, it 

 always gives rise to a sensation of sound. Perception-time is the 

 time required, for example, in colors, to decide what color it is and 

 in what part of the visual field it is located. The organs of special 

 sense differ from each other as to the number of separate excitations 

 that they can receive in a second. In reaction-time by the auditory 

 nerve the following things are involved: (1) the time consumed in 

 sound reaching the ear; (2) the time taken for the reception of the 

 stimulus by the sensory terminals of the auditory nerve and the 

 transmission to the higher centers, so that volitional impulse may be 

 started in the cerebral motor centers; (3) the time for the convey- 

 ance of those motor impulses to the nerve-cells of the spinal cord; 

 (4) the time necessary for the generation of impulses in the cells and 

 their transit down the motor nerves to the muscles of the hand ; (5) 

 the latent period of the contraction of those muscles. The reaction- 

 time for sound is about 0.150 second; light, 0.195 second; and for 

 touch, 0.145 second. Perception-time varies from about .01 to .02 

 second. 



THE GREAT SYMPATHETIC. 



The ganglia lying on each side of the vertebral column may be 

 divided into four parts, viz. : cervical, thoracic, abdominal, and pelvic. 



The cervical part of the great sympathetic is composed of three 

 ganglia. 



