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310 J. A. MACWILLIAM 



rections as the preceding, though not removed, since other and more 

 obscure factors remain. Stocks and Karn's figures show a remarkably 

 small increase of pressure with advancing age — from an average of 

 131 mm. at 20 years to 134 mm. in the group of 40 years and over 

 (average age, 49). 



It is warrantable to conclude from the concurrent evidence of the 

 extended statistical evidence now available that the idea of an extensive 

 progressive rise of systolic pressure in healthy persons as life goes on 

 is an erroneous one. It is clear that the rising pressure of childhood 

 undergoes accleration about puberty and attains what is approxi- 

 mately the adult level somewhere in the 17 to 20 period. There is 

 some evidence of a slight subsequent lowering — in the early years of 

 adult life. Apart from this, the pressure remains almost steady till 

 the age of about 40, after which a more definite rise progresses. But 

 the rise, though quite a definite one, is more limited in amount than is 

 commonly assumed; the total rise shown in the statistics, due to the 

 combined influences of age and increasing weight is on an average under 

 15 mm. The pulse pressure follows a course pretty similar to that 

 of systolic pressure under the influence of age. The available evidence 

 also bears weighty testimony to the relative constancy of systolic pres- 

 sures at different ages, when large numbers are dealt with and the 

 necessary allowances and corrections are made. It is clear, in view 

 of the foregoing averages, that the occurrence of exceptionally high 

 pressures in healthy persons must be relatively rare; otherwise the 

 averages would be much higher. The very moderate level of the 

 averages for middle and advanced life is all the more noteworthy in 

 view of the fact that the real ordinary pressures are likely to be over- 

 estimated rather than under-estimated, under the influence of nervous 

 excitement, etc. But while the averages for large numbers are rela- 

 tively constant, the fact of notable variation in healthy individuals 

 remains, the pressures in such persons being apparently set at levels 

 different from the ordinary — from causes that cannot at present be 

 adequately defined. The importance of hereditary influences has 

 been emphasised by numerous observers, e.g., Oliver (104), Dana (34), 

 Alvarez, Warfield (130) and others. 



With regard to the very high systolic pressures, S.200 to 250, some- 

 times (though rarely) met with in apparently healthy vigorous men 

 at such ages as 50, 55, etc., the mechanism of such pressures is well 

 worthy of careful investigation — with respect to the peripheral resist- 

 ance, capillary and venous pressures, blood volume, cardiac output, 



