NATURAL THEOLOGY. 177 



internally is their diffusion less universal. Blood- 

 vessels run along the surface of membranes, per- 

 vade the substance of muscles, penetrate the 

 bones. Even into every tooth we trace, through 

 a small hole in the root, an artery to feed the 

 bone, as well as a vein to bring back the spare 

 blood from it ; both which, with the addition of 

 an accompanying nerve, form a thread only a 

 little thicker than a horse-hair. 



Wherefore, when the nourishment taken in at 

 the mouth has once reached and mixed itself with 

 the blood, every part of the body is in the way of 

 being supplied with it. And this introduces an- 

 other grand topic, namely, the manner in which 

 the aliment gets into the hlood ; which is a sub- 

 ject distinct from the preceding, and brings us to 

 the consideration of another entire system of 

 vessels. 



III. For this necessary part of the animal econ- 

 omy an apparatus is provided in a great measure 

 capable of being what anatomists call demonstra- 

 ted, that is, shown in the dead body ; and a line 

 or course of conveyance, which we can pursue 

 by our examinations. 



First, the food descends by a wide passage into 

 the intestines, undergoing two great preparations 

 on its way : one in the mouth by mastication and 

 moisture — (can it be doubted with what design 

 the teeth were placed in the road to the stomach, 

 or that there was choice in fixing them in this sit- 

 uation?) — the other by digestion in the stomach 



