INFLUENCE OF THE NERVOUS SYSTEM. 305 



quantity of water in the secretions increased, but that there is 

 often a simultaneous augmentation of their solid constituents, 

 which are separated with them from the blood. The effete matters 

 undoubtedly often pass through this course more than once; thus 

 we frequently see iodide of potassium pass into the saliva (as wit- 

 nessed by myself), ferrocyanide of potassium into the gastric juice 

 (Bernard), arsenic, lead, and copper into the bile (Meurer and 

 others), and iron into the intestinal juice (Buchheim), all of which 

 often remain a very long time in the organism before they are 

 returned to the external world through the special organs of 

 excretion. The elucidation of the above relations is perhaps one 

 of the most important among the numerous interesting contri- 

 butions to science w r hich have resulted from the investigations of 

 Bidder and Schmidt, who have conducted these inquiries with 

 equal intelligence and perseverance. We shall revert to this sub- 

 ject under the head of " Nutrition," when we shall have to con- 

 sider the intermediate metamorphosis of matter that process 

 which to a certain degree is effected in the living organism, inde- 

 pendently of absorption and excretion. 



Important to physiology as is the knowledge of the influ- 

 ence exerted by the nervous system on the molecular movements 

 in the animal body, yet an inquiry of this nature, strictly speak- 

 ing, scarcely belongs to the domain of physiological chemistry, 

 seeing that we are still entirely ignorant of the chemical phe- 

 nomena which are associated with the function of the nerves. 

 Since, however, in the establishment of theories regarding animal 

 metamorphosis, the existence of the nerves and their influence on 

 the individual factors of this process have been almost entirely 

 ignored from a chemical point of view, it might not be wholly out 

 of place were we here to observe, that the more recent physio- 

 logical investigations have established beyond all doubt the direct 

 dependence of certain secretions upon definite parts of the nervous 

 system. 



We have already frequently had occasion to refer to Ludwig's* 

 important investigations in relation to the secretion of the saliva. 

 It appears from these observations, that there is not the slightest 

 amount of saliva secreted independently of the influence of the 

 nerves, and that the secretion is not effected indirectly by nervous 

 excitation, that is to say, through the agency of contractile parts 

 or by increased pressure of the blood-vessels, but directly through 

 the special influence of the nerves. 



* Op. cit. and Zeitschr. f. rat. Med. N. F. Bd. 1, S. 255-277- 



VOL. III. X 



