462 BIOLOGICAL PHYSICS 



when superabundant, and that the many openings, or 

 foramina, piercing the ethmoid bone are fulfilling the 

 great purpose of regulating the quantity of fluid within 

 the cerebro-spinal cavity, of maintaining the equilibrium of 

 intra-cranial and intra-spinal pressure, and of thus securing 

 the integrity of the important structures contained therein 

 the process of osmosis, with capillary circulation, being 

 utilised to effect the purpose. 



Generally, or at any rate often, a feeling or sensation is 

 experienced in the central nasal region for a more or less 

 brief period, and of more or less intensity, preceding the 

 act of sneezing. This feeling is excited by each and all 

 the stimuli or irritant influences capable of causing the 

 sneeze. But when a " cold in the head " is being caught, 

 it seems due to the operation or influence of a vis a tergo- 

 pushing the contents of the olfactory apparatus through 

 its neuro-capillary or terminal fibres. 



In controlling this outlet from the cerebro-spinal cavity,, 

 and acting as so many sphincters, so to speak, it appears to 

 us that an agency is provided in the muscular fibres distri- 

 buted within the structure of the Schneiderian membrane. 



The presence of these muscular fibres in the substance 

 of this membrane is difficult to explain, unless we concede 

 to them some such function, when, if we do so, their 

 presence at once becomes a part of a great plan, and is 

 recognised as a wonderful provision. We, therefore > 

 contend that they are, and act as, a series of sphincters, to 

 regulate the flow of the outpouring cerebro-spinal fluid, 

 and also that they act as guards against the entrance of 

 foreign particles from without. Hence the difficulty of 

 entrance through these channels of any except the smallest 

 of disease germs known to science, such as the influenzal, 

 but where an exit is allowed, however small, there must of 

 anatomical necessity be an entrance correspondingly small. 



Hence, also, the possibility of the entrance of such 

 minute organisms into the cerebro-spinal cavity by the 

 other channels numerable in this connection, viz. the pitui- 

 tary apparatus, the coccygeal mechanism, and the sweat 

 glands generally. 



The removal of offending particles from the surfaces 

 of the n.isal passages, for which an act of sneezing has 



