80 MAN AN ADAPTIVE MECHANISM 



important adaptation. That this is true of the act of 

 vomiting also is shown by the extreme difficulty with 

 which that reflex is dispossessed in the presence of 

 other stimuli. Vomiting occurs in the midst of deepest 

 emotion, of excruciating pain, during sleep and during 

 anesthesia, even up to the very moment of death, in 

 spite of the fact that it is attended by a widespread 

 muscular activity, during which the glottis is closed, the 

 diaphragm fixed, and the entire muscular apparatus 

 of the respiratory tract thrown into the most violent 

 contractions. Strangely enough, vomiting occurs al- 

 most exclusively among carnivora and omnivora, this 

 fact suggesting an interesting comparison of the hazards 

 of flesh with those of vegetable diet. 



In the adaptations of many animals to cold and heat 

 are to be seen some of the most characteristic re- 

 sponses to contact ceptor stimulation. Many animals 

 are provided with structural protection against cold and 

 heat by such variations in the body covering as fur, 

 feathers, hair, wool, layers of fat and pigmentation. 

 Among warm-blooded animals the most common reac- 

 tions to cold and heat are shivering, sweating and the 

 sensation of thirst. 



An interesting adaptation of birds to cold weather is 

 the phenomenon of " ruffled feathers," whereby in the 

 spaces between the quills a warm envelope of air is 

 retained around the body. Protection against cold 

 by the prevention of heat radiation is secured also by 

 the lowered respiratory rate which is common to most 

 animals when they come into contact with cold. The 

 habit of hibernation is an adaptation for protection 

 against starvation rather than against cold, since for 



