332 LECTURE XIV. 



everywhere do we find specific relations or affinities to 

 exist. If we cast our eyes upon the glands, it is a well- 

 known fact that there are specific substances, by which 

 we are enabled to act upon one gland, and not upon 

 another ; to rouse the specific energy of one gland, 

 whilst all the rest remain unaffected. In the case of 

 glands it is certainly much more difficult to exclude the 

 influence of the nerves, than in that of ciliated epithe- 

 lium, still certain experiments are recorded, in which, 

 after the section of all the -nerves, say of the liver 

 (Gr. Harting), it was found possible, by means of the 

 injection of irritating substances into the blood (these 

 being such as experience had shown to bear some inti- 

 mate relation to the organ), to provoke an increased 

 secretion in the organ. 



The discussion of this subject has, as you no doubt 

 are well aware, recently chiefly become centred in the 

 question of the irritability of muscle, a question which 

 has proved so difficult for the very reason that the pos- 

 session of irritability was restricted by Haller with great 

 exclusiveness to muscle. Haller with the greatest ob- 

 stinacy combated the opinion that any other part was 

 irritable ; and curiously enough he even contested the 

 irritability of parts, which, as the minuter investigations 

 of later observers have shown, contain muscular ele- 

 ments, as for example, the middle coat of the vessels. 

 Indeed, he made use of tolerably energetic expressions 

 when repudiating the excitability of the vessels, which 

 even then was maintained by others. I have already 

 informed you that there are large tracts in the vascular 

 system (for example, in the umbilical vessels of the foe- 

 tus, where they are particularly well marked) in which 

 enormous accumulations of muscular fibres are found, 

 but not a trace of any nerves. Here irritability exists 

 in a high degree ; we can produce contractions of the 



