COMPLEXITY OF GERMS.

New Zealand Herald, Volume LXVI, Issue 20244, 2 May 1929, Page 16

COMPLEXITY OF GERMS.

MAN AND HIS PARASITES.

PUZZLES FOR THE DOCTORS. NATURE'S MYSTERIOUS WAYS. Dr. J. 11. L. Cumpston, (ho Commonwealth Director-Genoral of Health, delivered in Canberra recently what is known as tho "Anno MacKenzio" ovation on preventive medicine, hut it. has received scant notice in tho press. Dr. Cumpston touched on many matters of importance to the nation, and parts of tho oration were of considerable interest, particularly what he, had to say regarding man and his parasites. "For many years after tho discovery of tho germ world," Dr. Cumpston said,

"it was believed that an acuto infection was the manifestation of an active visit to a human host of a germ parasite hungry for mischief and that, the attack over, the germ departed or died. The vagueness as to tho coming and going of tho germ still largely persists, but has been removed to some extent by the recognition that there are many peoplo who have minor attacks of the disease concerned so mild as to escape identification. In these persons the acute condition of reaction of the host to his parasite may slowly merge into a neutral state of parasitism or almost of toleration of the parasite by tho host, who, unaffected himself, may yet pass on tho germ to another who experiences an active attack. "Tho transition has become familiar to tho general public in the cases of diphtheria and enteric f.cver. Tho public understands that tho person who has apparently recovered from an attack of theso diseases may continue to harbour the parasites and may bo a menace to his fellows. The general public has even come to understand that a person may so harbour tho parasite without having had a previous attack. But tho public docs not so readily understand tho case of cerebro-spinal fever in which, in all probability, the great majority of tho cases show no cerebro-spinal symptom—these localised niaiiifestations developing in. only a very small minority of tho cases. An Interesting Paradox. "Tho complexity of the position is illustrated by tho following paradox. If a germ is virulent it rapidly destroys all its hosts, and as without hosts it cannot live it produces race suicide by its very vigour; but tho less activo do not kill their hosts but are able to produce a condition of toleration between host and parasite whereby tho survival of tho genu is assured. The germ most fitted to survive is obviously tho germ which is, apparently, tho least active in tho struggle for existence. The gerni, therefore. which in the end kills the largest number of victims is tho ono which least advertises its existence. It goes quietly on, living with and on its hosts, till some members of tho family reaching a susceptiblo human host attack and kill him, at tho same time ending their own existence. "Thcro can bo no doubt," said Dr. Cumpston, "that there is an association between cosmic factors and tho occurrence and recurrence of disease. For example, it was shown many years ago by patient observation that the annual rise of infantile diarrhoea occurred when tho temperature of tho soil had been gradually warmed by increasing summer to a critical point. Quito recently it has been .demonstrated that, while fleas are essential to tho spread of plague, and there can bo no malaria without mosquitoes, neither fleas nor mosquitoes can so operato unless tho humidity and the temperature of tho air are both at that optimum point necessary for tho occasion. Character of Epidemics. "This is an abstruse and difficult field. Ifc is undeniable that gco-physical agencies, 'earth-forces,' or whatever they may bo called, operate in some profound and fundamental way to produce, prevent or control disease, but as to the manner of their so doing wo are still in the dark . . . An organism, e.g., tho influenza organism, suddentiy becomes very active and virulent —at intervals perhaps of thirty years—and flares up into a worldwide epidemic, thereafter dying out as rapidly and becoming quiescent for another long period. "In its rapid transmission from ono person to another the organism acquires power till its zenith is readied and it rapidly becomes again a parasite of almost negligible importance. Ifc has also been definitely shown that in any population invaded hv an acute disease it never happens that all are killed, no matter how severe the disease; it is probable —though this is less certain—that all are not even attacked by the disease. Generally the disease, having attacked—and possibly killed—from one-third to onehalf of the population concerned, just fades into inactivity. Virulent and Minor Cycles.

"But apart from this behaviour of isolated epidemics there is another feature calling for attention. All are familiar with the fact that diphtheria, or measles, or any of the familiar infectious diseases is more frequent one year than another, but all are not equally familiar with the fact that, as well as these minor cycles at short intervals, these diseases show long cycles of extreme activity alternating with comparative inactivity. What determines these long cycles? Nobody knows. All that can bo guessed is that some change takes place in the nature or activity of the parasitic bacteria, but that is merely-begging the question." Dr. Cumpston added that an investigation had shown that a change had come over the rats of Bombay since the first appearance of plaguo at the beginning of this century. Whereas then a given dose of plague bacilli would have certainly killed all rats inoculated with it the same dose would now kill only one-fifth of fho number inoculated. .It was assumed that gradually tho susceptible rats were being killed off, the current breeding being only from tho immune stocks which had escaped infection. Laws for Communities. As far as man was concerned, added (he lecturer, in contrast to the immunity acquired by individuals as a result of invasion and attack by a particular parasite, there was the possibility that some persons had a natural immunity in some degree to certain parasitic bacteria. Assuming this to be so, it would be understood that continued infection by these bacteria would destroy tho susceptiblfs leaving this immune stock. By these people breeding tho community would tertd to become an immune community and so the disease would tend fo die out. This explanation was accepted by some authorities as a sufficient reason for the steady decline in the mortality from tuberculosis. It was clear that, Dr. Oumpslon remarked just as there were laws for the growth, development, decline and death of man as an individual so there were as exact and as comprehensive a series of laws for man as a, community. Tho community was a definite unit with its own laws, the nature of which was only now being dimly perceived.