CH. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 345 



spirits is the only one of these secretions absolutely necessary 

 to the action of the other animal forces in the economy (21); 

 and as they are secreted from the blood, this primary vital force 

 of the adult and perfect animal is dependent upon the cardiac 

 force. But the influence of the vital spirits on the heart keeps 

 up its continuous action, by means of its unfelt external impres- 

 sions (515, 532, note) ; and unless the cardiac nerves be filled 

 with the vital spirits, they cannot respond to the impressions 

 made on them by the blood, and consequently cannot excite 

 its whole motor force (665, 457). The two primary forces are 

 therefore reciprocally subordinate to each other : neither can 

 continue uninterruptedly, independently of the other, and if 

 the one ceases, so must also the other. Therefore, if there be 

 a common point of union of the two forces in an animal, that 

 point is also the general centre of the animal forces in the sense 

 already referred to (674). According to Lorry's observations, 

 this point is situate in that part of the meduUa oblongata cor- 

 responding to the second cervical vertebra. Animal life sud- 

 denly ceases if this portion be injured, destroyed, or removed. 

 ( Vide Haller's ^ Physiology,' part iv, vol. x, sect. 7, § 36.) 



677. The objections to this doctrine of the reciprocal sub- 

 ordination of the two forces to each other are easily met.—— 

 i. It may be advanced, that in the germ one of the forces must 

 necessarily begin to act before the other, and consequently 

 either the heart can act independently of the vital spirits, or 

 the latter may be produced independently of the heart. As 

 to the former objection, we answer, that both may commence 

 at once; as to the latter, the assertion is only applicable to 

 animals enjoying an independent existence, inasmuch as the 

 fluids may circulate before birth in virtue of extraneous forces, 

 and not of those proper to the germ (Haller's ' Physiology,' 

 § 891). 



ii. It is objected, that in sentient animals the heart's action 

 will continue for some time after decapitation. The reply is, that 

 the vital spirits do not drain away immediately after removal 

 of the brain ; and so long as the cardiac nerves respond to im- 

 pressions, so long are the vital spirits retained in them (515). 



iii. It is further objected, that the brain can perform sen- 

 tient actions after the heart has been removed from the body. 

 This may occur for a short time, but only so long as the brain 



