322 THE ACTIOX OF THE KERVES 



be inferred that tlirougli their intervention the pro- 

 toplasmic substance was excited to contract. But if 

 the capillary walls do not consist of protoi^lasm, such 

 a theory is altogfether inadmissible. 



Are they mdritive or secretory in their action ? — I 

 must ask the reader to consider with me whether it 

 is probable that these nerves are connected with 

 nutritive or secretory operations. IS^ow, although 

 many hig'h authorities still hold to the opinion that 

 nerves do act directly upon the nutritive procesS; 

 many considerations render it at least doubtful 

 whether the action of secreting cells is directly in- 

 flitenced by nerve-fibres in any case. Nutrition and. 

 growth and secretion are carried on at a rapid rate 

 in naany structures which are destitute of nerves, 

 and at every period of life. In disease the most active 

 nutritive changes occur in tissues which appear to be 

 wanting in nerve-fibres. For example, the formation 

 of pus from epithelium and the formation of tubercle, 

 can hardly be attributed to the influence exerted by 

 nerves, seeing that the phenomena occur in parts 

 to which nerve fibres do not reach, and yet the quan- 

 tity of nutrient matter taken up in a short time i^ 

 very considerable. Again, nutrition and growth are 

 most active in all living beings at a period of deve- 

 lopment anterior to that when nerves are formed. Se- 

 cretion is very active in glands which receive a limited 

 supply of nerves, and in those parts of glands to which 

 very few nerves are distribttted. Contrast, for ex- 

 ample, the jnultitudes of fine nerve-fibres ramifying 

 upon the stu-face of a sensitive mucous membrane, 

 vt'ith the few that can be traced around the uriniferous 

 tube, or followed to the follicles of the sebaceous 

 glands, or to those of the salivary glands. Pfliiger's 

 statements on this point have not been confirmed by 

 other observers, and from my own observations I am 

 convinced that if, as Pfliiger asserts, nerve- fibres are 

 distributed to secreting cells, they are arranged diffe- 



