478 PHYSIOLOGY CHAP. 



foetus is perfectly vitalised, so that its respiratory apparatus is 

 even at that time fully developed and ready to function. If, then, 

 during the last two months of pregnancy no respiratory acts are 

 performed under normal conditions, we may say that it is in a 

 state of apnoea, because having every aptitude 1'or breathing, it 

 does not breathe. 



At the end of 1858 Schwarz enunciated the doctrine that 

 foetal apnoea depends on the fact of the apnoeicity of foetal blood 

 in relation to the low excitability of the respiratory centres. The 

 foetus does not breathe, because the physiological cravings of 

 its tissues are amply provided for by the utero-placental gas 

 exchanges, but we must also admit that the excitability of its 

 respiratory centres is lower than in those of the mother, the 

 activity of which is maintained by blood of the same degree of 

 venosity as that which circulates in the foetus. 



The first respiratory act of the foetus is accomplished when any 

 cause whatsoever compresses the vessels of the umbilical cord, or 

 impedes access of the maternal arterial blood by the placenta. 

 This may occur even within the uterus, as Vesalius pointed out in 

 15-42. Under these conditions, if the interruption to the gas 

 exchange persists, the foetus may perish, asphyxiated within the 

 uterus. But if the venosity of the foetal blood develops slowly, 

 as when the mother is slowly dying, the foetal respiratory centres 

 gradually lose their excitability before ever they have become active. 



Under normal conditions the foetus begins to breathe when in 

 consequence of the expulsory act of parturition or detachment 

 from the placenta, the venosity of the foetal blood increases so 

 rapidly as to dispel the torpor of the respiratory centres. In 

 many cases, however, when by long travail the excitability of the 

 respiratory centres has become abnormally weakened, the high 

 venosity of the blood is not sufficient in itself to provoke the first 

 acts of respiration (asphyxial foetus). In such cases it is necessary 

 to start respiratory activity by employing accessory stimuli, 

 mechanical, thermal, or electrical (cold air, cold bath, slaps, elec- 

 trical shocks). 



Under conditions of normal excitability of the foetal respiratory 

 centres, the rapid increase of venosity in the blood suffices to cut 

 short the iutra-uterine apnoea at the moment of birth, as is 

 demonstrated by numerous authentic observations upon foetuses 

 that are still wrapt in their integuments, and sufficiently protected 

 from the cold of the air, and which yet begin to breathe at the 

 simple interruption of the place utal circulation, or ligature of the 

 umbilical cord. It is easy to repeat this demonstration on the 

 foetuses of rabbits or guinea-pigs (Engstrom). In the foetuses of 

 dogs taken from the uterus with the integuments intact, respiration, 

 on the contrary, does not begin regularly until the integuments 

 are lacerated (Pfliiger). In this case, then, besides the interruption 



