272 BIOLOGY. [Book ir. 



artificially provoked by the secretion of the vaso-motory nerves 

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

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

 activity. 



Incitations arising or provoked in the nervous centres, either 

 directly or by reflex action, can also transmit themselves to the 

 glandulai" vaso-motory nerves, and react on the secretion. Thus 

 we determine an abundant secretion in a dog, chained and 

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

 world knows likewise with what facility certain strong emotions 

 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. Schiffi had demonstrated that lesions of the cerebral 

 peduncles render the urine acid and albuminous. Punctures of 

 the roof of the fourth cerebral ventricle provoke saccharine 

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

 part of the cervical marrow can abolish the urinary excretion, 

 can produce anur'ia. 



Brief and incomplete though it may be, the exposition which 

 precedes suffices to make the mechanism and the importance of 

 secretion understood. We have therefore now passed in review 

 everything relating to nutrition, to its modes, to the diverse 

 biological contrivances which render it possible in the essential 

 being of 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. 



