LETTERS TO BROTHER JOHN. 131 



that juice or secretion which is called "saliva. " And 

 this increased secretion of saliva is the first of that 

 series of actions by which the nutrition of the body 

 is effected; and in this, the very first stage, you 

 see exemplified those three important properties of 

 which I have said so much in my two last Letters 



STIMULATION, SENSIBILITY, and CONTRACTILITY : 



for it is by virtue of their contractility that the 

 arteries supplying the salivary glands with blood, 

 and also constituting the gland itself, are capable 

 of acting; that is, of contracting and so of supply- 

 ing the gland with blood, from which blood the 

 saliva is to be secreted. It is by virtue of the sti- 

 mulating property of the food that their contracti- 

 lity is roused into action; and it is by virtue of 

 their sensibility that they are aware that a stimulus 

 is acting upon them. 



The nutritious bolus, then, having been thorough- 

 ly masticated and rolled about the mouth until it 

 has been well mixed up with saliva, is, by a very 

 complicated movement, mounted upon the back of 

 the tongue, and by it jerked into the throat, by 

 which it is propelled downward into the stomach. 

 Its presence in the stomach stimulates that organ, 

 as it stimulated the glands of the mouth ; and a 

 copious secretion of gastric juice (that is, stomach- 



