88o A MAX UAL OF PHYSIOLOGY 



tion is maintained through a tube passed through the glottis. 

 The eye reflexes disappear very quickly, and a period of high 

 blood-pressure immediately follows the occlusion. A fall of 

 pressure succeeds, due to vagus inhibition of the heart, and this 

 is followed by a second rise after the vagus centre succumbs to 

 the anaemia. Respiration stops temporarily (in twenty to sixty 

 seconds) after occlusion ; then follows a series of strong gasps, 

 and finally cessation of all respiratory movements. The blood- 

 pressure slowly falls to a level which is then maintained approxi- 

 mately constant for the remainder of the occlusion period. The 

 anterior part of the cord and the encephalon lose all function ; 

 no reflexes can be elicited from this part of the central nervous 

 system. The intra-ocular tension is much reduced, and the cornea 

 is characteristically wrinkled. 



When the cerebral circulation is restored by releasing the 

 vessels, the general arterial pressure soon begins to rise if the 

 period of occlusion has not overstepped the limit of successful 

 cardio- vascular resuscitation. The respiration returns suddenly, 

 the time of return depending on the length of the occlusion and 

 on other factors. The respiratory rate, at first slow, soon becomes 

 normal, and then more rapid than normal. The eye-reflexes 

 reappear more gradually ; the intra-ocular tension increases, and 

 the shrunken cornea becomes smooth and hard. The anterior 

 part of the cord recovers its functions gradually ; the reflexes con- 

 nected with it return, first the homonymous, then the crossed. A 

 short period of quiet follows ; then spasms of the skeletal muscles 

 appear, gradually increase in severity and extent, and termi- 

 nate in (a) death, (b) partial, or (c) complete recovery. In partial 

 recovery, disturbances of locomotion, such as walking in a circle, 

 paralysis, apparent dementia or loss of intelligence, and loss of 

 sight or hearing, may be observed. Voluntary movements of 

 the head, neck, shoulders, and fore-limbs have been seen eight 

 minutes after release from an occlusion of six minutes. Blindness 

 has been observed without loss of the pupillary light reflex. In 

 this case the visual cortex would seem to have suffered more 

 than the lower centres, an illustration of a general rule. 

 Complete recovery is rare after total anaemia lasting as much 

 as fifteen minutes, and has not been observed after an anaemia 

 of twenty minutes. Ten to fifteen minutes of total anaemia 

 represent the limit beyond which recovery of the brain, and 

 therefore successful resuscitation of the animal, cannot be 

 expected. 



Chemistry of Nervous Activity. Of this we are practically 

 ignorant. The percentage composition of the solids and the 

 percentage of water in the brains of three persons of different ages 

 are exhibited in the following table (W. Koch) : 



