106 ANIMAL-SENTIENT FORCES. [i. 



muscles perform, participate naturally in all these movements, 

 partly from sympathy, partly in consequence of a mechanical con- 

 nection (165, i, 161, 169, 179). Hence, the sensibility of muscles 

 is a very general principle in animal mechanism, since all these 

 movements are developed at each external impression and also 

 when it is felt, and the more vividly it is felt, the stronger the 

 movements (194, 165, iv); consequently, they must all be con- 

 sidered to be direct sentient actions of external sensations (163, 

 98), although they may be at the same time nerve-actions (183, 

 162). The muscles are excited to action by various external 

 impressions, as, for example, the urinary bladder by the injection 

 of water, the heart from the entrance of the blood, the bowels 

 by inflation with air, &c. The agreeable, or connatural external 

 sensations, maintain, sc^ far as they act on muscles, the order 

 and degree of movements and functions appointed by nature 

 to the muscles, and to the parts of the animal body regulated 

 in their function by them (195, 196). On the other hand, the 

 disagreeable excite contra-natural movements of the kind 

 mentioned. Tickling [Kitzel] excites vivid contractions; pain 

 excites sometimes violent cramps of a spasmodic character, 

 sometimes tetanic convulsions [Erstarrungen], which are also 

 occasionally caused by tickling. How direct sentient actions 

 from external sensations are induced in the muscular system 

 and in other parts of the body, and how they may be prevented, 

 has been already shown (129, 13 i, 136) ; and the doctrines have 

 an extensive application to pathology and therapeutics. 



205. The sentient actions which external sensations excite 

 in the other mechanical machines, may be deduced for the^ 

 most part from the preceding. External sensations act upoi 

 the blood-vessels, either through the heart, which is a muscle] 

 (167), or through their muscular fibres (168), or directly] 

 through the muscles which contain blood-vessels (169). lv\ 

 this respect, therefore, they can change the circulation. The 

 action on the blood-vessels, through their muscular fibres and 

 muscles, consists in a contraction of the blood-vessels (204), 

 (as is manifest in spasmodic attacks, which sometimes excite 

 congestion, sometimes accumulation of blood in parts not 

 implicated in the spasms). Probably, the nerves themselves 

 have the power of directly causing contraction of the vessels, 

 especially at their capillary terminations, as has been already 



