15 



tlir maternal structure^ .-in- calculated to produce these reflex actions; 

 l>ut tlir contact nf tin- sentient surface \vitl> the stiiiuilus in tho atmosphere itself 

 woiiM also excite it. And if tin- child should lie injured by tin' rude experii-ne.-s 

 incident il to |>.-irtiiritii>n. a yet more powerful means fur exciting tin- reflex 

 actions connected with respiration is furnished by the su.ldeii application of 

 cold t i the surface, as in sprinkling cold water upon it, or a sudden, shurp 

 slap with the open hand may lie substituted instead, as is commonly practised. 

 List, lnit not least, c.irlionie arid, ;LS it accumulates in .the blood, acts UK 

 a special stimulus to respiration. It cries out hi pain, and, presto! the 

 liemal mechanics is changed. The low pressure which is produced in the 

 aheoli by expansion of the lung's during inspiration compels xiiiinllnin-onn afflux 

 of air and blood in the alveoli ; while the high pressure which is produced l>v 

 tin- subsequent c-int ruction during e\]iinition causes *//////</<.,> efflux in 

 these tluids. which (low from high to low pressure in conformity with organic 

 law the one (lowing out liy retlux action through the route of ingress, the 

 oilier p.-is.,ii u into 'he left chambers of the heart and arterial system on its way 

 to the cell-liroo 1. as has already been described in the air-breather. This 

 I'.aiidonment of the old route for the new is readily explained, since it is in 

 sti ict accordance with physical law, l>eing in the direction of least resistance. 



For example, we /<<// the mechanics with high pressure in the arterial sys- 

 since this extends through tho ductus arteriosus to the semilunar valves of 

 the pulmonary artery, the floor of support to the arterial column. Hence, when 

 the alveoli expand during inspiration for sucking in air through the trachea, 

 the high pressure- in the pulmonary artery and ductus arteriosus compels this 

 blood to flow straight on to the low-pressure areas in the alveoli rimulianeaualy 

 \\ith the alflux of air, or in the direction of least resistance, in place of forcing 

 its way in the arterial system against high pressure, which would be contrary to 

 law. And the ductus arteriosus, though still filled with blood, as in the case of 

 an artery, beyond the ligature to where a collateral branch is given off, shrinks 

 an 1 contracts till it becomes a solid, impervious cord. 



For closing the foramen ovale the following mechanics apply: After birth 

 the inpour of blood in the left auricle by way of the pulmonary veins is as 

 rapid as it is in the right auricle through the venae cavse, and pressure is at 

 equilibrium in the two auricles, which at once suspends all tendency in the 

 lil ood to pass from one side into the other during auricular diastole ; whilst 

 during the auricular systole and the high pressure this produces hi the auricles 

 causes this blood to flow into the expanding ventricles, where low pressure 

 invites it, the same applying for either auricle. But gravitation also 

 should compel it in this direction, since the ventricles are under the auricles. 

 Thus a dual force applies (suction and gravitation) for compelling this blood in 

 the ventricles during the auricular systole, and the foramen ovalu, being thus 

 abandoned, is closed and obliterated by membranous formation. 



But in uitra-uterine life the matter is different ; here the whole blood is 



The intimate connection galisiuinu' iwtw.f i in.- r >:>! r. ,ui'l the glcin an Tun- ia of 



.!-> 'li'inninlratiiMi in tin 1 tulult liy tin 1 sann- IIH- i;is. Kur fxample, every impact of mid walrr 

 tin* akin i>r."'l !.'- <|i i~ n<> lir iuspinilinu or ex[> union ill tlie luiigi ; not deep, however, 

 l>ul very energeiir. 



