1006 MODIFYING CIRCUMSTANCES. 



power of the muscular tissue are much greater in 

 birds than in mammalia, and greater in the latter 

 than in reptiles or fishes, because birds are more 

 rapidly nourished. For the same reason, the 

 structure of the human brain is firm, dense, and 

 powerful, in proportion to the rapidity with which 

 its composition and vitality are renewed by the 

 formative process. Hence it is, that by far the 

 greater number of illustrious men have been dis- 

 tinguished no less by the capacity of the thorax 

 than for the size and configuration of the brain. 

 But if the chest be small, the lungs unsound, or 

 if respiration be diminished by impure air, im- 

 proper diet, intemperance, the depressing emo- 

 tions, intense thinking, and a sedentary life, the 

 vital properties of the blood are impaired, and 

 the brain imperfectly nourished ; so that although 

 large and well formed, its texture is infirm or 

 softened, and its power proportionally diminished. 

 If the skull be thick, (as in the African,) or 

 if the carotid and vertebral arteries are small, 

 the brain will receive proportionally less arterial 

 blood in a given time than when they are large ; 

 and still less when the chest is small, or the lungs 

 imperfect. All persons of this class belong to 

 the adynarnic temperament, whether the brain 

 be large or small. And owing to the softness of 

 its texture, the capillaries are easily ruptured, 

 giving rise to the effusion of blood or serum, 

 apoplexy, paralysis, or idiotism. It is therefore 



