84 ANIMAL-SENTIENT FORCES. [i. 



of its function to give existence to the animal forces, it differs as 

 little from the proper animal machines, and as necessarily be- 

 longs to them, as the roots of a tree to the tree itself (9, 11). 

 This mechanical machine is unique, for while it belongs to the 

 animal machines, it secretes the vital spirits from the blood 

 in its infinitely numerous minute canals, just as other secreting 

 organs secrete other fluids in their minute tubuli. Secretion 

 generally, as physiology teaches us, takes place according to 

 physical laws, rather than animal. But, nevertheless, since 

 the fluids entering the tubuli act as stimuli, and excite them to 

 the performance of their natural functions, as will be shown 

 subsequently (168, 172, 460), the natural function of the cortical 

 substance of the brain must be considered as animal ; only its 

 functions do not belong to the proper sentient actions, however 

 necessary and indispensable to them ; for, although requisite to 

 the production of material ideas in the cerebral medulla, it is 

 not a direct result of these, nor is it in itself a material idea, 

 since the secretion of the vital spirits is not directly caused 

 by conceptions (25, 97). Nevertheless, the cortical substance 

 can be influenced indirectly by sentient actions, as when con- 

 ceptions, desires, &c., influence the heart and the circulation ; 

 and thus, either by increasing or diminishing the amount of 

 blood sent to the brain, increases or diminishes the secretion of 

 vital spirits ; which phenomena are rather the results, however, 

 of sentient actions, than sentient actions themselves. It is 

 probable, although not established, that the material ideas in 

 the medullary substance exercise, as sentient actions, a direct 

 influence on the vessels of the brain. The brain receives at each 

 stroke of the left ventricle at least a sixth part of the whole 

 mass of blood, and this is distributed through every part of 

 • the brain, by means of the almost infinitely numerous capillaries 

 which enter into its substance (Haller), so that the smallest move- 

 ment in the brain would act almost necessarily on these minute 

 vessels. The vessels w^hich return the blood to the heart, the 

 source of vital movements (Lebensbewegungen), are equally 

 numerous. It is, therefore, probable, that the material ideas 

 in the brain, however hidden they may be from observation (28), 

 have some influence on the vital movements, independently of 

 the nerves, and that this may be one of the causes, why so 

 many conceptions, but especially painful sensations in the 



