20 THE ANIMAL MACHINES. [i. 



reference to the wliole animal kingdom, that the general animal 

 machines in which no species (so far as is known) is defective, 

 and which, consequently, are the most essential elements of 

 animal life, are the nerves, the ganglia, and the spinal cord, 

 with their (probably) accompanying cortical substance — or the 

 analogues of those structures — in which the vital spirits reside 

 and circulate ; and in which, in those cases, there is no cere- 

 bral cortical matter, the latter must be secreted directly from 

 the blood (11); and that the cerebrum and cerebellum, to- 

 gether with their cortical substance and the nerves of the 

 external senses, are not so general, and only essentially neces- 

 sary to certain species of animals, especially those endowed 

 with mind. Those only of the cerebrate animals, however, 

 which, without question, think and desire, are supplied with 

 a large and considerable brain; whilst those which manifest 

 ambiguous traces of ideas have a small, simple, and irregular 

 brain, differing little from the spinal cord, to which it appears 

 to be an appendage ; and, consequently, has probably only the 

 same functions. 



In this, the First Part of the Physiology, we investigate the 

 animal nature of the most perfect animals, in which all these 

 animal machines, or, at least, the most important, are com- 

 bined ; and which render them capable of acting in connection 

 with the thinking force. All other animals only differ, in 

 descending the scale, in a continually increasing defect in 

 the animal organs and forces ; and there are some whose whole 

 life is so simple and mechanical, that they scarcely manifest 

 any traces of the animal forces. In the Second Part of this 

 Physiology it will be shown how animal life can equally sub- 

 sist in these with only the most general and most essential 

 animal machines, and without the co-operation of those pecu- 

 liar to more perfect animals ; and it will be shown, also, how 

 far they are similar or inferior to the latter. Finally, the 

 Third Part will exhibit a general view of animal nature, and 

 will explain how the forces in each species of animal connect 

 the machines together, and complete animal life in each (8). 



