272 BIOLOGY. [BOOK n 



artificially provoked by the secretion of the vaso-motory nerve 

 or by the excitation of the vaso-dilatatory nerves, which seem t 

 exist at least in certain glands, has for result a greater secretor 

 activity. 



Incitations arising or provoked in the nervous centres, eithe 

 directly or by reflex action, can also transmit themselves to th- 

 glandular vaso-motory nerves, and react on the secretion. Thm 

 we determine an abundant secretion in a dog, chained an< 

 famished, by placing a piece of roast meat before him. All tht 

 world knows likewise with what facility certain strong e'motion; 

 act on the biliary secretion. These are examples of reflex phy 

 siological acts. The direct excitations of the nervous centres 

 can, in their turn, modify or trouble the secretions. As early as 

 1845 M. Schiff had demonstrated that lesions of the cerebral 

 peduncles render the urine acid and albuminous. Punctures oi 

 the roof of the fourth cerebral ventricle provoke saccharine 

 diabetes (Cl. Bernard). Lesions of the isthmus and of the lower 

 part of the cervical marrow can abolish the urinary excretion, 

 can produce anuria. 



Brief and incomplete though it may be, the exposition which I 

 precedes suffices to make the mechanism and the importance ofi 

 secretion understood. We have therefore now passed in review 

 everything relating to nutrition, to its modes, to the di verse i 

 biological contrivances which render it possible in the essential 

 being o'f complex organisms. Consequently we can forthwith 

 enter on the exposition of the chief properties of organised 

 matter. "We know how organised beings are nourished ; let us. 

 now see how they grow, and how they are reproduced. 



