612 Dynamic Theory. 



disgust in seeing, smelling or tasting something abominable. It can be 

 produced by tickling the fauces, or by the subcutaneous injection of tar- 

 tar (fmetic, &c. , also b}^ the dizziness arising from swinging, sailing, 

 riding backwards, &c. All of these stimuli, as well as those directly 

 disturbing the stomach by their offensive presence in it, appear to over- 

 flow into the pneumogastric system of nerves, and conve}- through it 

 the stimulus necessary to relax the cardiac sphincter muscle and allow 

 the regurgitation of the contents of the stomach. The simple disten- 

 sion of the stomach by a superabundance is enough to cause this re- 

 versal in infants and young children. In all these cases the action is 

 directly reflex, as regards the stomach itself, while as to the gullet it is 

 a sort of associated reflex action, the state of the stomach constituting 

 a stimulus which is carried to the nerve center from the stomach, and 

 back along several of the efferent branches of the pneumogastric at 

 once, a single stimulus thus affecting a group of motor nerves and pro- 

 ducing associated movements in several related and co-operating organs. 

 That the actions are governed from a common center, and are not di- 

 rectly dependent on each other, is shown by the fact that when vomiting 

 is caused by injection of tartar emetic into the veins, the reversed peris- 

 taltic action of the esophagus goes on even if it be separated from the 

 stomach. ( Carpenter. ) 



The act of sucking, by which all mammal infants, including man, 

 get their early supplies of fond, is purely reflex. An infant will suck 

 anything put into its mouth. And so will a calf or any other mammal 

 baby. The article in contact with the lips furnishes the stimulation by 

 touch, and the transmission of the stimulus to the medulla oblongata, 

 and from it to the various muscles concerned in the act of suction and 

 swallowing, is shared by several nerve trunks, the trigeminum, facial, 

 glosso pharyngeal, pneumogastric and hypoglossal, all perhaps having 

 something to do with it in one direction or the other. All this machin- 

 ery is set in motion in an unconscious infant. The same thing takes 

 place in those monstrosities which are sometimes produced, destitute of 

 cerebrum, which nevertheless breathe, and suck and swallow their food. 

 So, too, puppies from which the brain had been cut away, would suck 

 whatever was placed in the mouth. In the case of infant mammals 

 with all their faculties, it is not long before other stimuli come into 

 play to assist the one of touch upon the lips. As Carpenter points out, 

 the infant goes in search of its food, guided by the sense of smell, per 

 haps, and touch stimuli other than that of the lips. The actions are 

 still, however, reflex, although in the course of time they are accom- 

 panied by sensation. 



Beside the movements that are reflex from the medulla oblongata 

 alone, there is a long list in which the medulla is concerned in connec- 



