274 1'IIYSIOLOGY OF MUSCLES AND NERVES. 



briefly explained, <> each of the other processes of 

 automatic motion. We must content ourselves -with 

 the remark that an analogous conception of the nature 

 of the movements of the heart i.- probable, though DO 

 experimental proof of its correctness has yet been 

 aehieved. The cause of movements of the intestine is 

 not quite so difficult to understand ; at any rate, the 

 main principles found in the case of the nerve-cells of 

 the respiratory centre are valid in the case of all other 

 automatic centres. 1 Mention must still be made of 

 the fact that in the heart and intestine the nerve-cells 

 from which the automatic action proceeds are situated 

 within the respective organs themselves. For this 

 reason these organs can yet. exhibit movements after 

 the nerve-centres have been destroyed, or the organs 

 have been cut from the body. 



G. The tran-fen IK-', by means of the nerve-cells, 

 of an excitement from one nerve-fibre to another is 

 most clearly shown in that which is called reflec- 

 tion. By this term is meant the passage of an excite- 

 ment, which having acted on a sensory fibre has been 

 transmitted by it to the nerve-cells, to a centrifugal 

 fibre, by which it is conducted back from the centre 

 (as a ray of light is reflected from a mirror) and 

 makes Its appearance ;( t another point. The reflection 

 can occur either in a motor fibre, in which case it is 

 called a rell'-x action, or in a >eeivlory or relarda- 

 tory fibre. The former case is more common and 

 better known. As examples ( .f >urli reflex actions, I 

 may mention t he do-in;,' of the eyelids on the irrita- 



1 Tlmsc \vli<> \vi>h t<> ni it. -i in furthrr information as to these cir- 

 i-umst;ni<vs may ] tt - ri-frnvd to my work ]><'mirl\i<jcn iilirr die 

 Tliiil'njlu-it ili'r init<>nniti*i-/ii n .Y/vvr/f-iv//// 1 //, \o. KrlaiiLTdi, 1875. 



