AND FUNCTIONS OF ANIMALS, &C. 47 



distinction which we have been discussing will serve to 

 show how far the comparison, which this expression im- 

 plies, holds ; and vv^herein it fails. And, whether the dis- 

 tinction be thought of importance or not, it is certainly of 

 importance to remember, that there is neither truth nor 

 justice in endeavouring to bring a cloud over our under- 

 standmgs, or a distrust into our reasonings upon this sub- 

 ject, by suggesting that we know nothing of voluntary 

 motion, of irritability, of the principle of life, of sensation, 

 of animal heat, upon all which the animal functions de- 

 pend ; for our ignorance of these parts of the animal frame 

 concerns not at all our knowledge of the mechanical parts 

 of the same frame. I contend, therefore, that there is 

 mechanism in animals ; that this mechanism is as proper- 

 ly such, as it is in machines made by art ; that this me- 

 chanism is intelligible and certain ; that it is not the less 

 so, because it often begins or terminates with something 

 which is not mechanical ; that, whenever it is intelligible 

 and certain, it demonstrates intention and contrivance, as 

 well in the works of nature as in those of art ; and that it 

 is the best demonstration which either can afford. 



But, whilst I contend for these propositions, I do not 

 exclude myself from asserting that there may be, and that 

 there are otiier cases, in which, although we cannot ex- 

 hibit mechanism, or prove indeed, that mechanism is em- 

 ployed, we want not sufficient evidence to conduct us to 

 the same conclusion. 



There is what may be called the chemical part of our 

 frame ; of which, by reason of the imperfection of our 

 chemistry, we can attain to no distinct knowledge ; I 

 mean, not to a knowledge, either in degree or kind, similar 

 to that which we possess of the mechanical part of our 

 frame. It does not, therefore, afford the same species of 

 argument as that which mechanism affjrds; and yet it may 

 afford an argument in a high degree satisfactory. The gas- 

 tric juice ^ or the liquor which digests the f<x)d in the stom- 

 achs of animals, is of this class. Of all menstrua it is the 

 most active, the most universal. In the human stomach, for 

 instance, consider what a variety of strange su!)stances, and" 

 how widely different from one another, it in a few hours re- 

 duces to one uniform pulp, milk or mucilage. It seizes upon 

 every thin,^-. it dissolves the texture of almost every thing 

 that comes in its way. The flesh of, perhaps, all animals; 

 the seeds and fruits of the greatest number of plants ; the 

 roots and stalks and leaves of many, hard and tough as 



