458 THE RESPIRATORY MECHANISM. 



an influence on the blood-pressure, according to Owsjannikow, 

 extends from a point 4 to 5 millimeters above the point of the 

 calamus scriptorius to within 1 to 2 millimeters of the corpora 

 quadrigemina," says Professor Stewart, 22 who also remarks 

 that other observers give narrower limits, and adds: "Stimula- 

 tion of the medulla causes a rise, destruction of this portion 

 of it a fall, of general blood-pressure. There is evidently in 

 this region a nervous center so intimately related, if not to all 

 the vasomotor nerves, at least to such very important tracts 

 as to deserve the name of vasomotor center. Experiment has 

 shown that it is much the most influential center, and it is 

 usually called the chief, or general, vasomotor center. But 

 there are subsidiary centers all along the cord, and, while a 

 very large number of the constrictor fibers are related to the 

 chief center of the medulla, some are either normally under 

 the control of subordinate centers or may in special circum- 

 stances come to be dominated by them." If the floor of the 

 fourth ventricle is examined, the area comprised between "a 

 point 4 to 5 millimeters above the point of the calamus scripto- 

 rius to within 1 to 2 of the corpora quadrigemina" will be 

 found to include practically all the bulbar nerve-centers, so 

 that the "vasomotor center" may be said to include the bulbar 

 origin of practically all nerves. 



Again, it is manifest that the term "vasomotor" applies 

 to nerves distributed to vessels throughout the entire organism: 

 i.e., wherever terminal arterioles occur. If we now recall our 

 view that each general motor nerve distributed to a part sup- 

 plies it with its vasomotor fibers as well as with all others 

 distributed to it, unless associated with a special nerve, such 

 as the vagus, the deduction imposes itself upon us that the 

 vasomotor center in the medulla must coincidently be that of 

 the general motor nerves or at least the region where the 

 latter assume vasomotor functions. 



Even reducing the area represented by the vasomotor 

 "center" to the narrowest limits recognized by physiologists, it 

 may conservatively be said to include at least one-half of the 

 fourth ventricle. If we now ascertain the nerves involved in 

 this area, the suggestive fact asserts itself that this upper half 



a Stewart: Loc. cit., p. 158. 



