626 ANIMAL PHYSIOLOGY. 
gustatory subjective sensations are common, and must be re- 
ferred to the central nervous system. 
After the injection of some drugs subcutaneously, certain 
tastes are experienced. Persons born deficient in the sense of 
smell to a marked degree are very frequently also wanting in 
tasting power. — 
Comparative-—A mong the lowest forms of life it is extremely 
difficult to determine to what extent taste and smell exist sepa- 
rately or at all, as we can conceive of them. The differentia- 
tion between ordinary tactile sensibility and these senses has 
no doubt been very gradually effected. Observations on our 
domestic animals show that their power of discrimination by 
taste as well as by smell is very pronounced, though their likes 
and dislikes are so different from our own in many instances, 
At the same time we find that they often coincide, and it is not 
unlikely that a dog’s power of discriminating between a good 
beefsteak and a poor one is quite equal if not superior to man’s, 
and certainly so if his sense of taste, as in the human subject, - 
is developed in proportion to his smelling power. 
THE CEREBRO-SPINAL SYSTEM OF NERVES. 
I. SprnaL .NERVES. 
These (thirty-one pairs), which leave the spinal cord through 
the intervertebral foramina, are mixed nerves—i. e., their main 
trunks consist of motor and sensory fibers. But before they 
enter the spinal cord they separate into two groups, which are 
B Cc D 
Fic. 469.—Diagram of roots of spinal nerve illustrating effects of section (after Dalton). The 
dark regions indicate the degenerated parts. 
known as the anterior or motor and the posterior or sensory 
roots, which make connection with the anterior and posterior 
gray horns respectively. 
