464 BIOLOGICAL PHYSICS 



Further, in an act of sneezing we perceive that the 

 stimulus whatever it be if it be sufficiently strong to 

 determine the act (because it may be abortive, which often 

 happens) produces reflexly a closure or narrowing of the 

 pharyngeo-laryngeal spaces or passages by a contraction of 

 their encircling musculature, followed by a violent expira- 

 tory effort, with the effect that the expired air is made to 

 project into, and sweep through or traverse, the nasal 

 cavities, removing the cause of offence, or intensifying the 

 initial irritation. Two sets of muscles are thus brought 

 into action, viz. those that cause contraction of the upper 

 part of the respiratory tract, and those that produce a 

 violent act of expiration, the contraction of the former 

 being overcome by that of the latter. 



Along with the series of events occurring in an act of this 

 kind in the naso-thoracic regions, we find that a wide- 

 spreading disturbing influence is produced which makes 

 itself yW/ to the remotest extremities of the body, but 

 necessarily where its contents are most liquid, hence the 

 fluid contents of the cerebro-spinal spaces and inter-spaces, 

 amongst the others, are more or less violently set in 

 motion towards the periphery of their combined area or 

 extent, or particularly along the most yielding channels 

 connected therewith, two of which, in particular, are the 

 olfactory tracts, with their attached nerve endings. 



