7G ON THE STUDY OF PHYSIOLOGY. 



I shall adduce a few particulars, for the purpose of exem- 

 plifying the preceding remarks. 



A serpent swallows an animal larger than itself, which fills 

 its oesophagus as well as stomach, and of which the diges- 

 tion occupies several days, or even weeks. We open the 

 reptile during this process, and find that part of the animal 

 which remained in the oesophagus, sound and natural ; 

 while the portion which had descended into the stomach, 

 though still retaining its figure, is semi-liquefied, reduced 

 into so soft a state as to break down under the slightest 

 pressure. How effectually does this simple fact refute the 

 notions of digestion being mechanical trituration; or solu- 

 tion by heat (for the animal is cold-blooded) ; or the effect 

 of fermentation, or putrefaction, or coction ! 



The slow and languid motion of the blood in cold-blooded 

 animals has enabled us to demonstrate in them the circu- 

 lation, which in man can only be proved by argument. 



Physiologists have been much perplexed to find out a 

 common centre in the nervous system, in which all sensa- 

 tions may meet, and from which all acts of volition may 

 emanate ; a central apartment for the superintendant of the 

 hunvcm panopticon; or, in its imposing Latin name, ^ sen- 

 soriam commune. That there must be such a point they 

 are well convinced, having satisfied themselves that the 

 human mind is simple and indivisible, and therefore capable 

 of dwelling only in one place. The pineal gland, the corpus 

 callosum, the pons Varolii, and other parts, have been 

 successively suggested. Now, there are many orders of 

 animals with sensation and volition, who have none of 

 these parts : and this assumed unity of the sentient principle 

 becomes very doubtful, when we see other animals, pos- 

 sessed of nervous systems, which, after being cut in two, 

 form again two perfect animals. Is the immaterial prin- 

 ciple divided by the knife, as well as the body ? 



The heart has been regarded by many physiologists as 

 the prime mover in the animal machine — the origin of vital 

 motion in the embryo, the chief agent in forming and 

 maintaining the fabric, and the main-spring for keeping the 



