268 ANIMAL BIOLOGY 



habits and disease than by overwork. The continued 

 use of alcohol in excess generally leads to cardiac weakness. 

 Under the stimulus of a moderate amount of alcohol the 

 peripheral blood vessels become dilated; more blood 

 goes to the surface, and a feeling of warmth may be pro- 

 duced which, however, soon passes away. Alcohol proba- 

 bly produces disorders of circulation mainly through 

 its influence on the nervous system, thereby causing an 

 impairment of the proper nervous control of the heart and 

 blood vessels. Tobacco, especially when used by the 

 young, leads to heart weakness and palpitation, the 

 " tobacco heart" being a frequent result of the use of 

 tobacco in excess. 



