274 PHYSIOLOGY OF MUSCLES AND NERVES. 



briefly explained, to 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 is probable, though no 

 experimental proof of its correctness has yet been 

 achieved. 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.^ 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. 



6. The transference, 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 at another point. The reflection 

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

 called a reflex action, or in a secretory or retard a- 

 tory fibre. The former case is more common and 

 better known. As examples of such reflex actions, I 

 may mention the closing of the eyelids on the irrita- 



• Those who wish to obtain further information as to these cir- 

 curastances may be referred to my work Bemcrhnngcn iiher die 

 Thdtiglicit der autoinatischeti Ne?'ven- centra, &c. Erlangen, 1875. 



