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A MANUAL OF VETERINARY PHYSIOLOGY 



vessels occurs, but if the end in connection with the gland be 

 stimulated the vessels dilate, the arteries throb, and the blood 

 passes through the gland with such rapidity that the venous 

 blood becomes arterial in appearance. Much the same pheno- 

 menon occurs when the nervi erigentes, through which erection of 

 the penis is produced, are brought into activity. If these nerves 

 be divided there is no effect, but if the peripheral end be stimulated 

 the organ swells as the result of its enormously increased blood- 

 supply, and the blood flowing through the dorsal vein may now 

 be fifteen times greater in amount than in the quiescent con- 

 dition. 



Though it is clearly established that true vaso-dilator nerves 

 exist, there is still a great difference of opinion as to the extent 

 of their distribution. In most peripheral nerves, such as in the 



Fig. 39. — Blood-Pressure Curve of a Rabbit recorded on a Slowly Moving 

 Surface to show Traube-Hering Curves (Foster). 



The heart-beats are the closely situated up and down strokes, readily seen by 

 means of a lens. The next curves are those generally regarded as due to 

 respiration, the large bold undulations being the Traube-Hering curves. In 

 each Traube-Hering curve there are about nine respiratory curves, and in 

 each respiratory curve about nine heart -beats. 



nerves of the limbs, both dilator and constrictor effects may, 

 as has been mentioned, be obtained on stimulation, rapid induc- 

 tion shocks bringing about constrictor effects, slower shocks 

 producing dilator effects. If the nerve — say the sciatic — be 

 divided, the subsequent degeneration which follows affects the 

 constrictor fibres earlier than the dilator. There is good 

 reason for believing that the view originally held regarding 

 muscles possessing dilator fibres may have to be modified in the 

 light thrown on the matter by Bayliss, who has shown that 

 there are fibres in the superior roots of the cord, where the 

 axillary and lumbar nerves come off, which on stimulation pro- 

 duce dilatation of the vessels of the limbs. As these fibres are 

 running from the limbs into the cord, difficulty has been experi- 

 enced in explaining why stimulation should cause an impulse to 



