108 PHYSIOLOGY OF MUSCLES AND NERVES. 



found that certain of its fibres unite with those muscles 

 ^yhich pulsated. We already know that the other end 

 of the nerve is connected with the nerve-centre. If 

 the nerve is cut at a point between the irritated 

 spot and the nerve-centre, the muscular pulsation 

 occurs as before on the re-application of the irritant, 

 but the sensation of pain is absent. If, on the other 

 hand, the nerve is cut at a point nearer the periphery, 

 no muscular pulsation results from irritation, but pain 

 is felt. It thus appears that the peripheric nerves, 

 when irritated at any point in their course, are able to 

 cause effects both at their central and peripheric ends, 

 provided that the conductive power of the nerves re- 

 mains uninjured in both directions. This enables us 

 to study more closely the action of the nerves on the 

 muscles, by extracting and preparing a portion of the 

 nerve with its muscle, in an uninjured condition, and 

 then subjecting this nerve to further research. 



That a nerve is irritable, in the same sense as we 

 found that the muscle was, is already shown by these 

 preliminary experiments. But while it was possible 

 to observe the effects of the irritation on the muscle 

 directly, the nerve does not exhibit any immediate 

 change, either in form or appearance. Even under the 

 strongest microscopic power nothing is discernible, and 

 it would be impossible to know if a nerve is in any way 

 irritable if the muscle which occurs at one end of it 

 did not show by its pulsation that some change must 

 have occurred within the nerve. The muscle is there- 

 fore used as a re-agent to test the changes in the nerve 

 itself. The requisite experiments may be either with 

 warm-blooded or with cold-blooded animals. As, how- 

 ever, the muscles of warm-blooded animals, when with- 



