In certain parts of the American tropics there is found a rich gray moss growing in great profusion in these localities and on certain kinds of trees. It is not confined to any special level, but thrives best on low elevations. Under favorable conditions it grows at altitudes far above the surrounding swamps. Its character and quantity, however, are measured by the altitude at which it grows. It is an aërial plant, and it may be detached from the boughs of one tree and transplanted upon those of another. It may be taken with safety to a great distance, so long as an atmosphere is supplied to it that is suited to its nature, but when removed from its normal conditions and placed in a purer air it begins to languish and soon dies. If returned in time, however, to its former place or one of like character, it will revive and continue to grow. What element this plant extracts from the impure air is unknown. It cannot be carbonic acid gas, which is the chief food of plants, nor can it be any form of nitrogen. It is well known that the plant cannot long survive in a pure atmosphere. Whatever the ingredient extracted may be, it is certain that it is one that is deadly to human life and one that other plants refuse. Moisture and heat alone will not account for it. We have another striking instance in the eucalyptus, which lives upon the poison of the air around it. There are many other such cases in vegetable life; and while the animal is a higher organism than the plant, there are certain laws of life that obtain in both kingdoms and involve the same principles. Between the case of the gorilla and that of the plant there is some analogy. It may not be the same element that sustains them both, but it is possible that the very microbes which germinate disease and prove fatal to man sustain the life of the ape in the prime of health. The poison which destroys life in man preserves it in the ape. The chimpanzee is distributed over a much greater range than the gorilla and is capable of undergoing a much greater degree of change in food and temperature. The history of these apes in captivity shows that in that state the chimpanzee lives much the longer and requires much less care. From my own observation I assert that all these apes can undergo a greater range of temperature than of humidity. The latter appears to be one of the essential things to the life of a gorilla. One fatal mistake made in treating him is furnishing him with a dry, warm atmosphere and depriving him of the poison contained in the malarious air in which he naturally spends his life. Both of these apes need humidity. In a dry air the chimpanzee will live longer than the gorilla, but neither of them can long survive it; and it would appear that a salt atmosphere is best for the gorilla.