24 INTRODUCTION. 



through the arteries which convey it to its destined parts, by means 

 of their irritability and that of the heart. If these arteries be irri- 

 tated, they act more strongly, and propel a greater quantity of blood ; 

 the nervous fluid becomes more abundant and augments the local 

 sensibility ; this, in its turn, augments the irritabihty of the arteries, 

 so that this mutual action may sometimes be carried to a great ex- 

 tent. It is called orgasm^ and when it becomes painful and perma- 

 nent, inflammation. The irritation may also originate in the nerve 

 when exposed to the influence of acute sensations. 



This mutual influence of the nerves and fibres, either intestinal or 

 arterial, is the real spring of vegetative life in animals. 



As each external sense is permeable only by such or such sensible 

 substances, so each internal organ may be accessible only to this or 

 that agent of iri-itation. Thus, mercury irritates the salivary glands, 

 cantharides irritate the bladder, &.c. These agents are called spe- 

 cijics. 



The nervous system being homogeneous and continuous, local 

 sensations and irritation debilitate the whole, and each function, by 

 excessive action, may weaken the others. Excess of aliment 

 weakens the power of thought, while long continued meditation 

 impairs that of digestion, &c. 



Excessive local irritation will enfeeble the whole body, as if all 

 the powers of life were concentrated in one single point. 



A second irritation produced at another part may diminish, or 

 divert, as it is termed, the first : such is the eftect of blisters, pur- 

 gatives, &-C. 



Brief as our sketch has been, it is sufficient to establish the poss- 

 ibility of accounting for all the phenomena of physical life, from the 

 properties it presents, by the simple admission of a fluid such as we 

 have defined. 



Summary idea of the Functions and Organs of the bodies of 

 Animals, and of their various degrees of complication. 



After what we have stated respecting the organic elements of the 

 body, its chemical principles and acting powers, nothing remains 

 but to give a summary idea of the functions of which life is composed, 

 and of their appropriate organs. 



The functions of the animal body are divided into two classes : 



