732 INHIBITION OF REFLEXES. 



nose; inhibition of the movements usually elicited by tickling, by biting 

 the tongue. Especially strong irritation may even suppress the reflexes 

 coordinated for voluntary movement. Intense pain in the abdominal 

 organs (intestine, uterus, kidneys, liver, bladder) renders impossible the 

 act of walking or of standing. In the same category belongs the falling 

 down which follows injury to viscera richly supplied with nerves, and 

 which, either by involvement of motor nerves or by loss of blood, would 

 of itself be insufficient to account for the inability to maintain the 

 erect posture. Stimulation of the central organs through other centri- 

 petal paths (such as the organs of special sense, the sexual nerves, etc.) 

 diminishes the reflexes in other paths. 



4. During the discharge of an energetic reflex, such as ejaculation, 

 the production of less active reflexes, such as coughing, is suspended. 



5. Attention should also be called to the fact that inhibition of re- 

 flexes, whether through the will, or through the irritation of sensory 

 nerves, therefore by reflex action, is often attended with the excitation 

 of antagonistic movements. In some cases, further, it appears to be 

 sufficient to inhibit a reflex to concentrate the attention on the execu- 

 tion of such a complicated reflex movement in order to prevent it. 

 Some persons, for example, are unable to sneeze if they think intently 

 of the motor processes concerned; as the will, in a measure prematurely, 

 begins to control the reflex center by the thought, the normal course 

 of the reflex excitation for the stimulus from the periphery is interfered 

 with. 



6. Certain poisons, such as chloroform, picrotoxin, morphin, quinin, 

 potassium bromid, and others, diminish reflex irritability, probably 

 after a transitory increase. A constant current passed longitudinally 

 through the spinal cord enfeebles the reflexes, particularly a descending 

 current. If a frog be paralyzed by asphyxia in air free from oxygen, 

 the brain and the spinal cord are w r holly unirritable and are, therefore. 

 incapable of reflex excitation. The motor nerves and the muscles, 

 however, suffer little impairment of irritability, even after the lapse of 

 several days. 



According to the method of Turck the degree of reflex irritability in decapi- 

 tated frogs is tested by estimating the time that elapses between immersion of 

 the foot in dilute sulphuric acid and withdrawal of the part. After application of 

 blood to the optic lobes or after irritation of a sensory nerve, the time is in- 

 creased. 



Setschenow differentiates the reflexes into tactile, or those that are elicited 

 by irritation of tactile nerves, and pathic, or those resulting from irritation of 

 sensory (pain-transmitting) fibers. He believes, with Paschutin, that the tactile 

 reflexes are inhibited by the will, and the pathic by the center described by him. 



Theory of Reflexes. The following theory has been proposed to explain the 



phenomena observed in connection with reflex movements. It is believed that 



the centripetal fiber, in the transmission of the impulse conveyed through 



it encounters considerable resistance within the gray matter, with the ganglion - 



;lls of which it is contact on all sides through the fibrous network of the gray 



matter. The least resistance is in the direction of those motor nerves that make 



their exit at the same spinal level on the same side. In this way the weakest 



irritation gives rise to the simple reflex, which in general can be recognized as a 



simple protective or defensive movement with respect to the seat of sensory 



timulation. In the direction of other motor ganglion-cells the conduction of 



the impulse encounters still greater resistance. In order for the reflex to be trans- 



:d also along these paths, either the stimulus must be considerably increased 



increasing strength and duration of the stimulation the reflex' movement 



may increase in extent) , or the resistance in the course of the conduction between 



