EXPERIMENTS ON VERTEBRATES 143 



high. Goltz had already shown, moreover, that the 

 frog deprived of its cerebral hemispheres avoids ob- 

 stacles. The same holds good for the fish that has 

 lost the cerebral hemispheres. The first act in taking 

 food thus consists in an optical reflex. As soon as 

 the food comes in contact with the palate it arouses 

 swallowing reflexes. These reflexes are completed 

 by means of the vagus group. According to the 

 segmental theory these reflexes should still be possi- 

 ble even when all the parts of the brain lying in front 

 of the nuclei of the vagus have been removed. Such 

 is the case. As long as the medulla oblongata is 

 preserved the frog swallows the food that is put into 

 its mouth. 



The respiration of frogs is chiefly mouth- and neck- 

 respiration. The corresponding nervous segments 

 for these parts of the body lie in the medulla oblon- 

 gata and in the beginning of the spinal cord. If the 

 latter be severed behind the noeud vital (calamus 



\ 



scriptorius), as Schrader found, all the muscles whose 

 nerves originate behind the place of division continue 

 to participate in the respiration coordinately. 



It was formerly assumed that the compensatory 

 movements of frogs were dependent on organs of the 

 mid-brain. Schrader found, however, that frogs 

 whose brain had been extirpated as far as the medulla 

 oblongata (the origin of the acusticus) still showed 

 compensatory movements. The earlier physiologists 

 were deceived by accidental effects of the operation. 

 For the sake of completeness it should be mentioned, 



