He entered the Customs and Salt Department of the Government of Bombay in April 1876, and served in Kharaghoda (the Dustypore of the Tribes), Uran, North Kanara and Goa Frontier, Ratnagiri, and Bombay itself. In May, 1903, he was appointed Chief Collector of Customs and Salt Revenue at Karachi, and in November, 1905, was made Superintendent in charge of the District Gazetteer of Sind. He retired from the service in August 1906.
He married in 1883 the daughter of the Rev. J. Chalmers Blake, and left a family of two sons and three daughters.
In 1902 he was deputed, on special duty, to investigate the prevalence of malaria at the Customs stations along the frontier of Goa, and to devise means for removing the Salt Peons at these posts, from the neighbourhood of the anopheles mosquito, by that time recognised as the cause of the deadly malaria, which made service on that frontier dreaded by all.
It was during this expedition that he discovered a new species of anopheline mosquito, which after identification by Major James, I.M.S., was named after him Anopheles aitkeni. During his long service there are to be found in the Annual Reports of the Customs Department frequent mention of Mr. Aitken's good work, but it is doubtful whether the Government ever fully realised what an able literary man they had in their service, wasting his talent in the Salt Department. On two occasions only did congenial work come to him in the course of his public duty—namely, when he was sent to study, from the naturalist's point of view, the malarial conditions prevailing on the frontier of Goa; and when during the last two years of his service he was put in literary charge of The Sind Gazetteer. In this book one can see the light and graceful literary touch of Eha frequently cropping up amidst the dry bones of public health and commercial statistics, and the book is enlivened by innumerable witty and philosophic touches appearing in the most unlikely places, such as he alone could enliven a dull subject with. Would that all Government gazetteers were similarly adorned! But there are not many "Ehas" in Government employ in India.
On completion of this work he retired to Edinburgh, where most of the sketches contained in this volume were written. He was very happy with his family in his home at Morningside, and was beginning to surround himself with pets and flowers, as was his wont all his life, and to get a good connection with the home newspapers and magazines, when, alas! death stepped in, and he died after a short illness on April 25, 1909.
He was interested in the home birds and beasts as he had been with those in India, and the last time the writer met him he was taking home some gold-fish for his aquarium. A few days before his death he had found his way down to the Morningside cemetery, where he had been enjoying the sunshine and flowers of Spring, and he remarked to his wife that he would often go there in future to watch the birds building their nests.
Before that time came, he was himself laid to rest in that very spot in sure and certain hope of a blessed resurrection.
The above imperfect sketch fails to give the charm and magnetic attraction of the man, and for this one must go to his works, which for those who knew him are very illuminating in this respect. In them one catches a glimpse of his plan for keeping young and cheerful in "the land of regrets," for one of his charms was his youthfulness and interest in life. He refused to be depressed by his lonely life. "I am only an exile," he remarks, "endeavouring to work a successful existence in Dustypore, and not to let my environment shape me as a pudding takes the shape of its mould, but to make it tributary to my own happiness." He therefore urges his readers to cultivate a hobby.
"It is strange," he says, "that Europeans in India know so little, see so little, care so little, about all the intense life that surrounds them. The boy who was the most ardent of bug-hunters, or the most enthusiastic of bird-nesters in England, where one shilling will buy nearly all that is known, or can be known, about birds or butterflies, maintains in this country, aided by Messrs. B. &. S., an unequal strife with the insupportableness of an ennui-smitten life. Why, if he would stir up for one day the embers of the old flame, he could not quench it again with such a prairie of fuel around him. I am not speaking of Bombay people, with their clubs and gymkhanas and other devices for oiling the wheels of existence, but of the dreary up-country exile, whose life is a blank, a moral Sahara, a catechism of the Nihilist creed. What such a one needs is a hobby. Every hobby is good—a sign of good and an influence for good. Any hobby will draw out the mind, but the one I plead for touches the soul too, keeps the milk of human kindness from souring, puts a gentle poetry into the prosiest life. That all my own finer feelings have not long since withered in this land of separation from 'old familiar faces,' I attribute partly to a pair of rabbits. All rabbits are idiotic things, but these come in and sit up meekly and beg a crust of bread, and even a perennial fare of village moorgee cannot induce me to issue the order for their execution and conversion into pie. But if such considerations cannot lead, the struggle for existence should drive a man in this country to learn the ways of his border tribes. For no one, I take it, who reflects for an instant will deny that a small mosquito, with black rings upon a white ground, or a sparrow that has finally made up its mind to rear a family in your ceiling, exercises an influence on your personal happiness far beyond the Czar of the Russias. It is not a question of scientific frontiers—the enemy invades us on all, sides. We are plundered, insulted, phlebotomised under our own vine and fig-tree. We might make head against the foe if we laid to heart the lesson our national history in India teaches—namely, that the way to fight uncivilised enemies is to encourage them to cut one another's throats, and then step in and inherit the spoil. But we murder our friends, exterminate our allies, and then groan under the oppression of the enemy. I might illustrate this by the case of the meek and long-suffering musk-rat, by spiders or ants, but these must wait another day."
Again he says, "The 'poor dumb animals' can give each other a bit of their minds like their betters, and to me their fierce and tender little passions, their loves and hates, their envies and jealousies, and their small vanities beget a sense of fellow-feeling which makes their presence society. The touch of Nature which makes the whole world kin is infirmity. A man without a weakness is insupportable company, and so is a man who does not feel the heat. There is a large grey ring-dove that sits in the blazing sun all through the hottest hours of the day, and says coo-coo, coo, coo-coo, coo until the melancholy sweet monotony of that sound is as thoroughly mixed up in my brain with 110° in the shade as physic in my infantile memories with the peppermint lozenges which used to 'put away the taste,' But as for these creatures, which confess the heat and come into the house and gasp, I feel drawn to them. I should like to offer them cooling drinks. Not that all my midday guests are equally welcome: I could dispense, for instance, with the grey-ringed bee which has just reconnoitred my ear for the third time, and guesses it is a key-hole—she is away just now, but only, I fancy, for clay to stop it up with. There are others also to which I would give their congé if they would take it. But good, bad, or indifferent they give us their company whether we want it or not."