HEREDITARY PREDISPOSITION TO DISEASE. 213 



that hereditary predisposition is to be dreaded. The 

 obstacles which it throws in the way of permanent 

 recovery are even more formidable, and can never 

 be entirely removed. Safety is to be found only in 

 avoiding the perpetuation of the mischief; and, 

 therefore, if two persons, each naturally of an ex- 

 citable and delicate nervous temperament, choose 

 to unite for life, they have themselves to blame for 

 the concentrated influence of similar tendencies ia 

 destroying the health of their offspring, and subject- 

 ing them to all the miseries of nervous disease, 

 madness, or melancholy. 



Even where no hereditary defect exists, continued 

 excitement of the nervous functions in the mother, 

 from anxiety, grief, or other causes, during preg- 

 nancy, has often a striking effect on the future men- 

 tal health and constitution of the offspring. Many 

 authors testify to the truth of this fact, which has 

 not escaped the penetration of some mothers. The 

 Margravine of Anspach observes justly, that " when 

 a female is likely to become a mother, she ought t<? 

 be doubly careful of her temper ; and, in particular, 

 to indulge no ideas that are not cheerful, and no 

 sentiments that are not kind. Such is the con- 

 nexion between the mind and body, that the features 

 of the face are moulded commonly into an expres- 

 sion of the internal disposition ; and is it not natural 

 to think that an infant, before it is born, may be 

 affected by the temper of its mother?" Memoirs, 

 vol. ii. chap. viiL 



The second condition required for the health of 

 the brain is a due supply of properly oxygenated 

 blood. The effects of slight differences in the 

 quality of the blood are not easily recognised, but 

 when extreme they are too obvious to be over- 

 looked. If the stimulus of arterial blood be alto- 

 gether withdrawn, the brain ceases to act, and sensi- 

 bility and consciousness become extinct. Thus, 

 when fixed air is inhaled, the blood circulating 



