Not only do children suffer in the tropics, but the men over fifty do not stand the climate as well as the young. The proper age to go to the tropics is in the time of the greatest physical vigor, from twenty to thirty years of age, and it is not very safe even then.

These rules are borne out by the results of an examination of the ages of a regiment of soldiers divided into classes as to whether they stand the climate (1), deteriorate (2), break down (3), or die (4). The following table presents the percentages:

Age

Percentage

1

2

3

4

17-20 .........................................................

66

17

5

12

21-25...........................

65

26

7

2

26-30...........................

69

18

10

3

31-35...........................

56

28

11

5

36-40...........................

52

26

13

9

41-45...........................

65

12

17

6

46-50........................................

50

17

17

17

51-55...........................

33

67

Men below thirty have an advantage in preserving their health; from thirty to thirty-five there is less chance and men over thirty-five are at a disadvantage. The boys below twenty and those from twenty to twenty-five are about on a par as to their ability to retain health, but the younger die or break down where those twenty to twenty-five merely deteriorate in health. Twenty-six to thirty seems to be the most resistant age, as it has the highest percentage who retain their health. Over thirty progressively more break down. The percentage of deaths increases from twenty-five up, as we would expect. Our soldiers, then, should be twenty to thirty for tropical service; younger than this they die more frequently, over thirty they deteriorate more frequently, and over thirty-five break down and die in greater numbers also. Nevertheless, the figures show that the advantage of youth is not so very great, as it is probably counterbalanced by the greater discretion of maturity. Old men should stay at home, and none over fifty-five, or, better, none over fifty be sent out - still better, none over forty-five.

* Report as Consul in Manila, July 2, 1898, "Blue Book," pp. 330-1, advising an influx of 10,000 Americans, who " all can live well and become enriched".

The 1908 Report of the Surgeon General presents similar statistics, and Burot & Legrand, in their work on Tropical Hygiene, state that experience shows that soldiers less than twenty-two do badly in the tropics, and that many of the boys of eighteen or nineteen sent out never return. He places the minimum at twenty-three, and M. Morache places the limit at twenty-five, because the maximum resistance to fatigue and disease is between twenty-five and thirty-five. They advocate retirement after fifteen years service, and that every soldier be retired before forty years of age, unless he be a non-commissioned officer, when it may be lengthened to forty-five years of age. Colonization is impossible where the young and old cannot safely live.

Tropical Anaemia

Tropical edema is a swelling or dropsy of the lower extremities generally from knees down and due to cardiac weakness. It is the condition we find in cooks, policemen and others who have to be on their feet, and whose circulation is thus dammed back by the constant hydrostatic pressure which in other people is relieved by other exercises or being occasionally seated. But in tropical residents there is a dwindling of all the muscles, including the heart, so that there is almost universally a condition of cardiac weakness, and this is sufficient to cause the dropsy. We should call this condition the tropical heart, because it is so common.

Tropical anaemia generally refers to the anaemia due to intestinal parasites (anchylostomiasis), but there is an anaemia in all people of over two years' residence and in many who have been there but one year. It is part and parcel of the general exhaustion we have mentioned, and not due to infections. It is practically universal, and deserves more investigation to discover whether it is a real reduction of number of blood cells or a chlorotic condition of lessened hemoglobin. It is particularly noticeable when a transport arrives, and we can compare the newcomers with the veterans.

All these conditions increase tropical exhaustion, and we have thus proved that permanent residence of white men in our tropical dependencies is wholly out of the question, for it results in a neurasthenia which unfits for further work. Our contact with the natives must be kept up by officials who go there for limited terms.

Tropical neurasthenia, by the way, is the identical condition called American nervousness, and due to the same causes, the unfitness of Northern types to the climate, and is found more frequently in blonds as a matter of course.