THE TROPICAL AGRICULTURIST. [September i, 1888 
The Influence of Black Colouring.*— " It would 
seem at first sight that the black Bkin should 
rather be a disadvantage than otherwise ; but in 
the reality it is not so. The black colour of the 
skin causes it to absorb more heat than a white 
skin, but while it is doing so, at the same time 
and for the same reason it is giving off more heat 
— its absorbing power and also its radiating power 
being greater. Therefore, when the sun's rays im- 
pinge upon the skin, the heat is rapidly absorbed ; 
but, as the rate of absorption of heat is greater 
than the rate of radiation, unless the temperature 
of the skin were lowered by some other influence, 
the whole surface of the body would become ex- 
tremely hot. 
" To complete the explanation, we must here take 
into consideration what is known of black-skinned 
men. Any one who has been in India can see that 
natives, although they drink water freely, do not 
appear to perspire so copiously as Europeans, but 
this is simply because more of the perspiration 
comes from them in the form of vapour, and 
less is seen to stand like dew-drops on the 
surface of the skin. In the evaporation of the 
moisture exuding from the skin, we have a de- 
mand for heat far greater than an ordinary ob- 
server might imagine ; and by it all the surplus 
heat which the black skin absorbs over and above 
what it gives off by radiation can be disposed of. It 
is a fact which few realize, that the amount of 
water is small indeed which, by being evaporated 
could transform into its latent condition all the heat 
derived from the warming influence of the sun in the 
hotest climates." 
In a communication, which I have received since 
the above was written, from Professor von Helmholtz, 
Berlin, he says, "I do not know any physical ex- 
Elanation of it," — the advantage of the presence of 
lack skin. "An analogous fact, certainly, is what I 
have often seen in Switzerland, that light coloured 
men, who do not become brown in the sun, get 
blistered and become covered with eruption by the 
reflection of the sun from the snow-fields; while 
those who become brown bear it much better. The 
black pigment generally lies in the deeper epithelial 
layers. Perhaps the nerve ends or other parts of 
the living tissue are sensitive to the deep piercing 
rays of the sun, and the violet and ultraviolet rays, 
which are usually most powerful in all chemical 
actions, are kept off by the brown pigment. It is 
known, also, that in frogs and chameleons the shift- 
ing black pigment moves to the surface as if the 
outer layers of the tissues had to be protected." — 
Translated. 
While everyone must admit that the above re- 
marks are conclusive of the view expressed by Pro- 
fessor Huxley of the extremely complicated nature 
of a full solution of this question, yet I cannot see 
that they are incompatible with my own theory 
which referred to the part played by absorption, 
radiation, and evaporation. f 
* From a paper communicated by the author to the 
Boyal Society of Edinburgh on 5th December 1887. 
t Darwin in Animals and Plants under Domestication, 
ohap. xxi.,says: — "Light-coloured animals suffer most 
from insects, in Thuringia the inhabitants do not like 
grey, white, or pale cattle, because they are much more 
troubled by various kinds of flies than the brown, red, 
orblaok cattle." "In the West Inditsit is said that 
' the only horned cattle fit for work are those which 
have a good deal of black in them. The white are 
terribly tormented by the insects, and they are weak 
and sluggish in proportion to the amount of white.' " 
Although nothing is said of tbo colour of skin, the 
remarks evidently refer to white-haired animals possess- 
ing white skins i nder the white coat, and most prob- 
ably belonging lu the genus Bos taunts. Again, 
" white pigs suffer from scorching by the sun." Spcak- 
)n<» of catt le, he says : — " Oases have been published of 
cutaneous diseases with much constitutional disturbance 
Cin one instance after exposure to a hot sun), affecting 
every single point which bore a white hair, but com- 
pletely passing over other parts of !Lo body. Similar 
A NEW ENEMY OF CINCHONA IN JAVA. 
A correspondent writes : — "The Indische Mercuur 
of 21st July opens with the ominous heading 
' Een Nieuwe Piaag der Kina Boomen,' — ' A New 
Plague of the Cinchona Trees.' With their never 
failing courage and determined perseverance, the 
resolute de Kuiters and Tromps of cultivation 
look the evil fairly in the face, and set about 
their struggle against the new enemy with the same 
undaunted energy with which they made 
' The firm connected bulwark * * * 
Spread its long arms amidst the watery wave, 
Scoop out an empire, and usurp the shore.' 
Kessler's little work shows that there is no diminu- 
tion of their annual perseverance in the cause of 
science, and as they were the first to set the 
example of introducing the healing plant into the 
East, let us hope that they will now meet with 
the success they well deserve in the resistance of the 
new enemy." 
♦ 
LETTERS PEOM JAMAICA :— No. 23. 
Blue Mountain District, Jamaica, 
For packet of 18th July 1888. 
Dear Sib,— My last letter was despatched by 
the packet of 9th ultimo ; this will, I trust, go for- 
ward by the " Orinoco," the newest steamer of the 
Royal Mail Co. She is, I believe, perfect as re- 
gards all modern improvements, though not nearly 
as large as the grand P. & O. steamers which 
have, I noticed, enabled you to get letters in 
Colombo in only 15 days from London, The West 
Indies are still far behind the East; it takes us 
usually 17 days to get our home letters, as the 
steamer goes first to Barbadoes, which is cer- 
tainly a deviation, but if ever the Panama or 
Nicaragua Canals are opened, our mails will be 
accelerated. 
Our crop season has been unusual in being very 
backward, and before we have finished with the 
upper fields, we are likely to have commenced 
in the lower, for there are fully 2,000 feet dif- 
ference between the lower and upper portions of 
this plantation. The coffee in the lower fields 
appears to be forward, but it will be a small crop 
generally because of the long drought which lasted 
from the end of November to the middle of 
April, and dried up much of the blossom ; 
the settlers consequently will not do . as well 
as last year, both as regards quantity and 
prices, for those who sold in cherry made money; 
those who bought largely must have lost a good 
deal of money. In the Blue Mountains pro- 
per we still have a good deal of green coffee 
on the trees, some of which will not be ripe till 
cases have been observed in horses." I have no doubt 
but that bad Darwin been the observer of the details 
of those cases he records, he would have discovered 
that the areas affected, though very closely correspon- 
ding to the areas coated with white hair, were yet 
more nearly identical with the areas of white skin. It 
should be understood that the areas of white hair and 
of white skin do not exactly correspond iu our own 
cattle. Some British cattle that are mostly white under 
the white hair have black or brown patches or spots 
away from coloured hair of any kind, and not notice- 
able until the hair is turned up. Again, the darker skin 
prevailing under dark spots, extends often an inch or 
more under the surrounding white hair. Only a small 
percentage of cows that are practically white haired 
have the black skin predominating. 
