LETTERS TO BROTHER JOHN. 87 



when you consider the literal meaning of the word, 

 you will have no difficulty in understanding that 

 modified sense in which it is used in the language 

 of science. It means, literally, a long stick with a 

 sharp point, with which husbandmen were wont to 

 goad their oxen along, in times and countries when 

 and where oxen were used for agricultural purposes. 

 Now these properties, contractility and sensibi- 

 litythese important properties, upon which, it is 

 manifest, life depends ; and without a healthy con- 

 dition of which the health of the body can no more 

 be preserved than the true motions of a watch can 

 be maintained with a broken or otherwise injured 

 main-spring these properties, I say, are subject to 

 certain laws. I am now about endeavouring to 

 establish these laws ; or rather, I am going to en- 

 deavour to convince you of their existence. That 

 they do exist, is a truth that has been well and in- 

 controvertibly established and admitted among all 

 men acquainted with the animal economy, the effect 

 of medicines upon it, &c. &c., ever since Hippocra- 

 tes practised physic at Athens; and that is more 

 than two thousand years ago. But it is not suffi- 

 cient that medical men are aware that these laws 

 exist; my object is, to convince you of their exis- 

 tence. I want you to know what is good, and what 



