1871.] 



Change of Climate on the Human Economy. 



313 



which carry on the functions of animal life being most affected, especially- 

 such as form the great bulk of the body. It would be difficult to say 

 whether the watery part of the blood and body generally is reduced by ex- 

 cessive perspiration. The osseous system and thoracic and abdominal viscera 

 are probably little changed. The fibrous and gelatinous are perhaps more 

 altered; but it would be difficult to separate this from the change in the 

 fatty muscular and nervous tissues, the three doubtless most of all affected. 

 In warm latitudes less fat is required than in cold ones to keep out cold and 

 generate internal heat or muscular force. Hence nature uses it up in its 

 vital processes, and thus first gets rid of what does not itself play a vital 

 part in the human economy, or materially influence health by its removal, 

 and would only prove an encumbrance. The prevalent languor of body 

 and mind no doubt arise partly from diminished energy in the nervous and 

 muscular tissues ; but are they not also, and perhaps principally, due to a 

 decrease in their bulk, similar to that in other tissues 1 Strength is the 

 manifestation of muscle acted on by nervous influence ; and, from several 

 experiments made on the officers and crew of H.M.S. * Bristol,' strength 

 decreases and increases with the foregoing changes in weight — a fact which 

 goes far to prove that though loss of strength may be partly of nervous 

 origin, the muscular tissue is also largely involved in its production, and 

 is probably both physiologically weakened and physically altered in 

 texture*. 



The cause of this reduction in weight in the tropics is threefold : — first, 

 a diminished necessity for surplus fat, which becomes absorbed ; second, 

 that peculiar and not easily explained physiological effect of heat, which 

 causes the tissues to decay faster than in cold latitudes ; third, diminished 

 lung-work and blood-oxygenation, and thereby an imperfect renewal of 

 tissue. On the other hand, the languor and weakness are due, first, to loss 

 and relaxation of the muscular substance ; second, to a similar loss of 

 nervous tone and matter ; third, to suboxidation of the blood f, which 

 impairs the activity not only of the muscles, but of the nerve-centres which 

 originate, and nerve-cords which transmit motor and sensory impressions ; 

 [and, fourthly, in their early stage, to a reduced supply of their vital stimu- 

 lant the blood, diverted from the internally situated nerve centres, nerves, 

 and muscles, to the cutaneous surface. — Feb. 27.] The early and primary 

 results of tropical warmth on the tissues are probably chiefly physical and 

 quantitative ; but when prolonged, especially if conjoined with an erroneous 

 diet, their composition is affected, and they are also chemical and qualitative. 



What are the true bearings and diagnostic value of this closely-allied loss 

 of weight and strength 1 Are they solely physiological ? or when do they 

 become pathological ? Do they always, or at what stage do they indicate 



* These data were scarcely ample enough for tabulation. The ship's motion, imper- 

 fect testing apparatus, and difficulty of finding one equally suited for all men, in whom 

 the best-developed sets of muscles often differ, make this a troublesome inquiry. 



t Proceedings of the Eoyal Society for 1870, No. 122, p. 520. 

 VOL. XIX. 2 B 



