BLOOD PRESSURE IN THE TROPICS. 329 



influences which the abdominal vessels, enervated by the splanchnic 

 nerves, may exert upon the general blood pressure. 



Vasomotor tone is influenced by a number of known agencies and it 

 is often markedly affected by reflexes of remote origin, which often may 

 not be determined in a given case. 



Insomnia is often associated with hypertension, and the opposite 

 condition usually prevails during somnolence. Certain conditions of 

 what may be called the higher neuroses are accompanied by increased 

 blood pressure, while certain forms of neurasthenia show a hypotension. 



Cutaneous and other peripheral vasoconstriction and increased pressure 

 due to cold, as well as the opposite condition due to heat, are recognized 

 facts which suggest a jDrobable influence of this nature in the etiology 

 of the lowered pressure in the Tropics. 



It does not seem improbable that this lowered pressure might be 

 explained by lowered peripheral resistance in two ways. While the 

 secretory function of the skin is increased in the Tropics, it is doubtful 

 if this is at the expense of increased resistance, in fact, logically quite 

 the contrary may be expected, and the normal surface resistance and 

 vasomotor tension necessary to produce the required surface heat of 

 temperate climates, in the Tropics is greatly diminished the year around, 

 and in certain seasons is reduced almost to nil. This decreased vaso- 

 motor tone may logically be expected to lead to the opposite condition, 

 or to one of stasis which could explain not only some of the variations 

 in mean systolic pressure, but might equally explain the condition of 

 clinical anaemia mentioned above, as well as some of the neurasthenias, 

 cerebral anaemias, and acute oedemas of dependent portions of the body 

 which are so prevalent in the Tropics. Another factor which must be 

 taken into consideration is the possibility of splanchnic influences. When 

 we remember the enormous influence which the' splanchnic vasomotor 

 tone has upon the general blood pressure, and particularly upon the 

 portal circulation, and also that it is a proved fact > that abdominal 

 pressure has a marked influence on the general mean aortic tension, the 

 "tropical liver" and the very prevalent sensation of abdominal vacuity 

 which are partially responsible for the very general tropical custom of 

 abdominal binders may have some scientific foundation. 



Gastrointestinal disturbances with secondary clinical manifestations 

 are exceedingly prevalent in this country and it is but reasonable to 

 suppose that these conditions may produce vasomotor disturbances of 

 sufficient magnitude to exert some influence upon the general blood 

 pressure, principally through the portal circulation and splanchnic tone. 



In conclusion, we again wish to state that much of the discussion in 

 this paper is hypothetical and offered simply to call attention to the 

 possibilities of continued research in an extremely interesting field in the 

 study of medicine in the Tropics. 



96475' 6 



