PLATE 4 



EXPLANATION OF FIGURES 



Fig. 10 Blood from an excited horned toad was injected .sul)Cutaneously into 

 this animal at the point indicated by the arrow. The skin has l^ecome clearly 

 paler around the point of injection. X 1. 



Fig. 11 At tlie point indicated by the arrow, 0.2 cc. of a solution of one part of 

 adrenalin chloride in 10,000,000 parts of 0.75 per cent NaCl was injected under the 

 skin of the horned toad. The skin has become paler at this point, producing an 

 effect identical with that obtained by injecting blood from an excited horned toad 

 into the animal shown in figure 10. X 1. 



Fig. 12 Into the horned toad on the left was injected 0.2 cc. of a solution of one 

 part of adrenalin chloride in 100,000 parts of 0.75 per cent NaCl. The pale colora- 

 tion produced by this means may be contrasted with the usual coloration illus- 

 trated bj' the animal on the right. X 1. 



330 



