" PNEUMATIC SPACES" 531 



prevent disaster, while a see-saw, or compensatory agency, 

 may thus be established between the cutaneous surface 

 of the face and head and the lining membrane of these 

 cavities, whereby pressure on the encephalon is obviated 

 under circumstances in which that pressure might be 

 liable to disturbance ; thus a simple " pallor of the 

 cheeks " may be followed and counterbalanced by a 

 "delicate blush," the " marble blanch of profound shock" 

 by a " scarlet suffusion," compensation being effected by 

 the alternate opening and closing, or vice versa, of the 

 appropriate external and internal blood channels external 

 and internal sweating^ alternately cutaneous ly and naso-pharyn- 

 geally, may in like manner, and for like purposes, occur. 

 We have in such provisions, therefore, supplemental 

 intra-cranial pressure safeguards and protections in these 

 environments of the cranial contents. 



It may also be here stated, that the sounds produced 

 and the minute shocks conveyed by the process of 

 mastication, as well as the noise created by the acts 

 of deglutition and phonation, seem to be softened down, 

 and made more bearable for the organs of sense and the 

 brain above. 



The anatomical and histological aspects of the subject 

 of the olfactory nerves and their use as an excretory 

 mechanism, having elsewhere been pretty fully dealt 

 with, we have, therefore, on this matter, only a few 

 observations to make in supplement. It is said that 

 the olfactory trunks, which are hollow in many animals 

 throughout life, and in the human species up till adult 

 age has been nearly reached, become closed, as life advances 

 beyond that period. This may be so, but we apprehend 

 that closure^ so called, is only clogging, and hence a matter 

 of degree ranging between partial patency and complete 

 occlusion. 



This view may be sufficient to account for the frequent, 

 we might almost say the copious, and regular nasal dis- 

 charge in the young, and the comparative absence of it, 

 at least the more fluid part of the discharge, in the 

 grown-up and aged. 



Thus, we perceive that the very active period of life, 

 when the nervous system is most plastic, and when 



