STIMULI AND THEIR ACTIONS 



359 



extremities by contracting their muscles, and stands, sometimes 

 more than an hour, in this grotesque position (Fig. 152, B). By 

 the proper operations it can be determined that by the mechanical 

 stimulation of the skin the ganglion-cells at the base of the mid- 



FIG. 152. Frog that has been deprived of his cerebrum. A, In the customary squatting attitude. 

 B, In the attitude of general reflex tone ; the muscles of the limbs and the back are in 

 constant contraction, so that the frog stands immobile upon his raised legs in the attitude of 

 a frightened cat. 



brain are put into a tonic state of excitation, which is communicated 

 to all the body-muscles that are innervated from that point. 1 



The after-effects of many chemical stimuli, especially the 

 bacterial poisons, are the most interesting and of most practical 

 importance. It is an old experience that after recovery from certain 

 infectious diseases, such as small-pox, scarlet fever, and measles, 

 the bodies of men and animals are immune to further infection 

 from the same source. It is well known that the modern thera- 

 1 Cf. Verworn ('96, 5). 



