328 MUSGEAVE AND SISON. 



The volume determinations of these two points have not, so far as we 

 know, been made on any large series of people in the Tropics, and any 

 opinion as to the presence or absence of anaemia as determined by these 

 methods at the present time would be speculative. 



However, to judge from the data which are available, it is much more 

 logical to explain the clinical anaemia as being due to diminished periph- 

 eral resistance and lack of the demand for a supply of blood to furnish 

 heat to the skin than it is to assume the condition to be one of true 

 anaemia dependent upon the greater concentration and diminished volume 

 of blood, with a concomitant decrease in actual amount of haemoglobin 

 and in the total number of red blood cells. 



The hypothesis offered in this paper that the anaemia is a clinical one 

 only is borne out by its very evanescent character, for when patients, 

 particularly children, in whom it is shown most markedly, are transferred 

 to a cooler climate which requires a greater volume of cutaneous circula- 

 tion, and which also increases the vasomotor tone, the clinical anaemia 

 disappears with a rapidity which argues against the supposition that it is 

 due to an actual poverty of the blood. Children who appear to be anaemic 

 not infrequently develop normally tinted skins and mucous membranes 

 within a very few days after having started on an ocean voyage or even 

 after having been transported to the cooler climate of Baguio. 



PERIPHERAL RESISTANCE. 



Alterations in peripheral resistance as a direct result of the greater 

 and continuous heat of the Tropics offer an attractive hypothesis for the 

 explanation of lowered blood pressure in this climate and the confirmation 

 of such an hypothesis would greatly simplify the study of the etiology 

 of that exceedingly prevalent condition, tropical neurasthenia, as well- 

 as that of several other generally prevalent tropical clinical entities 

 which usually are considered to be of climatic origin. 



The preponderating influence of peripheral resistance in maintaining 

 blood pressure is a proved fact. Unless some counterbalancing change 

 in the force of the heart occurs, increased resistance raises the pressure 

 and decreased resistance is followed by a lowering of the pressure. 



Claude Bernard established a vasomotor influence over peripheral 

 resistance, 'and it is now known that this resistance, both arterial and 

 venous, is largely under vasomotor control and that the vasoconstrictor 

 fibers are those which are principally concerned in this phenomenon. 

 Furthermore, vasomotor tone, in particular of vascular areas, constantly 

 varies in response to local needs; increased function always being ac- 

 companied by increased blood flow. If such an area be of sufficient 

 extent and the increase is not compensated for by vasoconstriction in 

 other vascular locations, a fall in mean aortic blood pressure follows. 

 The most striking example of this condition is found in the great 



