88 



TROPICAL CLIMATOLOGY 



cells of the papillary layer of the corium. In negroes the pigmenta- 

 tion is deeper and more diffusely spread in the epidermis. 



(2) Vascular Modification.— Associa.ted with pigmentation there 

 is said to be a persistent dilatation of the vessels and capillaries of 

 the skin, and it is stated that hair and nails grow more rapidly in 

 the tropics than in the Temperate Zone. 



Light in general is believed to have an effect upon the blood, 

 which absorbs the violet and ultra-violet rays, and the red 

 corpuscles under these influences probably absorb more 

 oxygen. 



(3) Disease. — With regard to disease, there appears to be no 

 reason to doubt that the irritating effect of light has at least a part 

 in the aetiology of Kaposi's disease {Xeroderma pigmentosum), 

 which we have met with in the tropics, where it would naturally 

 develop rapidly in children prone to the disease. 



There is also no doubt that these rays play a part in the pro- 

 duction of the erythema of pellagra, as will be described later on, 

 •and they may have some effect in producing sunstroke. 



Woodruff draws attention to the almost universal neurasthenia 

 of white men in the tropics, among whom he says insanity is more 

 common than in Temperate Zones. In support of the latter state- 

 ment, he asserts that the insanity rate in the Philippine Army in 

 1901 was 2-02 per mille, while in the United States from 1889-1898 it 

 was 1-13; but he remarks that the diagnosis was not confirmed on 

 the arrival of several of the Philippine soldiers in the United States, 

 as they recovered en route. He draws attention to the loss of 

 memory in the tropics {tropical amnesia), a condition which is very 

 prevalent on the West Coast of Africa, being often called ' coast 

 memory.' He also mentions the midday siesta as useful in pre- 

 venting this neurasthenia, and in this he is also probably correct, 

 especially for ladies. Ordinary officials and business men, however, 

 cannot afford to rest in the middle of the day. 



Moon's Rays. — The extravagant stories by old writers, and 

 especially the tales given by sailors with regard to the influence of 

 the rays from the full moon, have thrown such discredit upon this 

 subject that we have been unable to find any literature seriously 

 considering the effects of its rays upon man. 



Nevertheless, in our own experience, the rays of the full moon 

 do produce headache and a certain amount of nervous irritability in 

 persons who sleep in the open. The subject requires and deserves 

 scientific study. 



ACCLIMATIZATION. 



Plehn seems to have been the first careful observer clearly to prove 

 that the changes induced in the new-comer as he enters the tropics 

 in due course disappear, and his organs becoming accustomed to the 

 new work demanded from them, he virtually returns to the same 

 condition of temperature, respiration, etc., as in the Temperate 

 Zone — in other words, becomes acclimatized. Further, if constantly 



