486 ANIMAL PHYSIOLOGY, 
of the cerebral cortex has been removed, the reflexes are much 
more prominent than before. Experience teaches us that the 
acts of defecation, micturition, erection of the penis, and many 
others, are susceptible of arrest or may be prevented entirely 
when the usual stimuli are still active, by emotions, etc, 
These and numerous other facts tend to show that the higher 
centers of the brain can control the lower; and it is not to be 
doubted that pure reflexes during the waking hours of the 
higher animals, and especially of man, are much less numerous 
than among the lower vertebrates. The cord is the servant of 
the brain, and a faithful and obedient one, except in cases of 
disease, to some forms of which we have already referred. 
Certain recent experiments show in the clearest way how the 
conditions of the central nervous system, and especially in the 
first instance, the brain determines the reflex time to which we 
shall presently refer: thus, among other influences, music and 
even different airs greatly alter the reflex-time, and, indeed, 
the whole character of the act (tendon-reflex). 
It is not to be supposed, however, that the processes that 
are clearly cerebral, and which modify normal reflexes so 
greatly, are all of the nature of inhibitions, or that they are 
at all fully understood. They are unquestionably very complex 
in nature, and probably too intricate to be completely un- 
raveled. 
Reflex Time.—One of the most satisfactory methods of ascer- 
taining the length of.time a reflex act occupies is the follow- 
ing: Let an electric stimulus be applied to one of the eyelids, 
whereupon both blink. The whole interval, minus the latent 
period of the orbicularis muscle and the time occupied in the 
transmission of the necessary nervous impulses over the nerves 
concerned (the fifth and facial) to and from the centers involved 
(medulla), gives the duration of the processes in the brain-cells. 
The whole period in one instance was ‘0662 seconds, which, re- 
duced as indicated, gives ‘0555 as the time required for the 
changes that take place in the brain-cells. 
It will, of course, be understood that at best these figures 
are but an approximation, owing to several possible sources of 
error; also that, as has been already stated, the actual period 
varies with the condition of each subject at the time of ex- 
periment, not to mention the variations for individuals and 
groups of animals. In the instance chosen the brain itself was 
the center involved, but the same laws apply to the reflex 
mechanisms of the cord. 
