other animals such as horses, sheep, goats, pigs, rabbits, mice, guinea-pigs, &c., having been proved to be unsusceptible even when inoculated with diseased blood. 2. That the disease is naturally transmitted by the cattle tick (Ixodes bovis), and, so far as we at present know, by this means alone.

One has only to be seized with the latter fact, and accept the dictum, "No ticks, no fever!" to realise that a knowledge of the particular species of tick which carries the disease is essential to a complete understanding of so complicated a trouble.

In the following pages the cattle tick (Ixodes bovis), its habits and lifehistory, will be considered first, and at some length. Before doing so, however, I propose, at the risk of being considered tedious, to discuss ticks in their relationship to other animals-not, of course, as parasites, but as a branch of the great animal kingdom.

Students of the structure, habits, and relationships of animal to animal are known as zoologists, and the sorting out or arranging of animals together into natural groups is called "zoological classification. There are two kinds of classification in the ordinary sense of the term-an artificial classification and a natural classification.

These may be illustrated by books. For example, we are given a large number of books and asked to classify them. If we do so artificially we can arrange them by their size, their colour, or their binding. Of such a classification what would be the possible results? A volume of Spurgeon's sermons sandwiched in between the work of a Huxley and a Byron. In a natural classification things would be quite different. Historical works would be found together, poetical works would be found together, and so on. This classification would even go further, for the historical works of France would be sorted by themselves and not jumbled together with those of England and Germany.

It will be seen that a natural classification" entails a knowledge of the contents of the books being dealt with; in fact, a "a looking into" of their

natures.

So with the classification of animals. Where could we get a better illustration than a whale. At first sight we would classify a whale as a fish, but this is not the case. The whale is adapted for living in the water, and a study or "looking into" of its nature places it amongst such animals as cows, horses, &c., a branch of the animal kingdom (mammalia), of which man himself is the head.

The differences between a whale and a fish are these: The fish is a coldblooded creature and breathes through gills; the whale has warm blood, and, as most of us are aware, has to come to the surface of the water periodically to breathe fresh air. Again, a fish is covered with scales, whilst a whale's clothing, although very scarce, is typical hair. And, lastly, a fish lays eggs, whilst a whale produces its young alive, and, moreover, suckles them.

Classification.

Animals are first grouped in Sub-kingdoms, which are divided into Classes, these again into Orders, the orders into Families, the families into Genera, and the genera into Species.

Thus, for example, we have a large number of dogs exactly alike, such as the Newfoundlands. These constitute a Species.* Then we have the Aus

*It is now generally believed that the majority of the numerous "breeds" of domestic dogs are varieties, all descended from a common ancestor-probably a domesticated wolf.

tralian dingo, or wild dog, which forms another species called familiaris australis, and then again there are the wolves, constituting the species lupus.

These three species, with others, form a Genus called Canis, which is closely related to the genus Vulpes (the foxes), and the genus Megalotis (containing the dog-like fennecs of North Africa).*

The three Genera, Canis, Vulpes, and Megalotis, make up the Family Canide (the dog family). The dog family has amongst its relations the Felidae, or cat family (cats, tigers, lions, &c.), the Hyanide, or hyæna family, and the Mustelide, or weasel and badger family.

These families, together with the bear family and others, constitute the Order Carnivora, or flesh-eaters.

Of the numerous Orders, some of the best known are the Insectivora, or insect-eaters (ant-eaters, porcupines, &c.); the Marsupialia, or pouchbearers (opossums, kangaroos, &c.; the Rodentia, or gnawers (rats, mice, &c.), which, together with the Carnivora, are grouped together, and form a Class, Mammalia, the members of which, it will be noticed, are all animals which suckle their young.

There are only four other Classes :-(1) Aves-feathered animals, which lay eggs and hatch them by the warmth of their own bodies (the birds); (11) Reptilia-scaly-coated creatures which lay eggs, leaving them to be incubated either by the heat of the sun or that arising from decaying vegetable matter (snakes, lizards, turtles, &c.; (III) Amphibia-slimyskinned animals, which in their young stages are fish-like, living in water, and breathing through gills, but which subsequently acquire true lungs, and develop limbs suitable for locomotion on land (frogs, newts, &c.); (IV) Pisces-those scaly or naked animals, which live all their lives in water, and breathe through gills (the fishes). These five Classes collectively form the great sub-kingdom Vertebrata, and include all animals possessed of backbones and true skeletons.

The sub-kingdom Vertebrata has been purposely chosen to illustrate the outlines of classification, because its members, if not numerically the greatest, are certainly the most conspicuous and best known to everybody, whereas the other sub-kingdoms, in their different ramifications, are more or less obscure to any but the scientific investigator.

Another sub-kingdom of which mention is made in speaking of one of the phases of tick-fever, is the Protozoa. The members of this sub-kingdom are microscopic animals, composed of jelly-like matter (protoplasm). They reproduce by fission; that is, by breaking up into parts, which parts themselves maturing, again divide, and so on. They differ from the rest of the animal kingdom in that they present no structural elements, and are considered as the lowest forms of animal life forming the connecting link with the vegetable kingdom. The "micro-organisms" referred to later on are referable to this division.

Classifying "Ticks."

In order to determine the position of these small animals, it is necessary to consider another sub-kingdom called Arthropoda, which, in point of popular knowledge, comes nearest to the Vertebrates.

It is usual when referring to an animal to give both the name of the genus and the species. The name of the genus-which may be likened to a surname is always followed by the specific name, which supplies the baptismal name. For instance, the dingo belongs to the genus Canis, and the species familiaris-australis. It is, therefore, always referred to as Canis familiaris-australis, which is the Latin for the native dog of Australia.

The term is derived from two Greek words, arthron, a joint, and pous, a foot. The sub-kingdom comprises those animals with jointed limbs, having no back-bones or true skeletons; they have, however, an external skin composed of a hard, horny substance, which takes the place of the true skeleton seen in the Vertebrates, and to the inner surface of which the muscles are attached.

This outer shell is made up of as the "pseudo-skeleton."

of a series of segments or joints, and is spoken

The sub-kingdom Arthropoda is naturally divided into four well-defined classes (1) Insecta (true insects); (11) Myriopoda (centipedes and millepedes); (II) Arachnida (scorpions, spiders, and mites); and (IV) Crustacea (crayfish, crabs, and lobsters).

Many Arthropoda are spoken of as "insects" and for the purposes of economic and popular entomology, it is a suitable designation. The oft-told story of the railway official who allowed a pet tortoise to travel free, because it was an insect," illustrates, however, one of the many curious uses to which the word is often put.

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Strictly speaking, the word "insect" is only applied to the members of the class Insecta, those jointed-limbed animals which have the body divided into three distinct regions, viz. :-(1) the head, (II) the thorax or chest, and (III) the abdomen. The head bears two antennæ, whilst to the central portion or thorax are attached six legs, and nearly always one or two pairs of wings.

The second class, Myriopoda, is easily distinguished by the numerous legs of its members, of which they never have less than eight pairs.

The members of the third class, Crustacea, are nearly all aquatic animals, possessing two pairs of antennæ and the peculiar power of reproducing lost limbs.

The fourth and last class is the Arachnida, which comprises those modified insects having eight legs, and the body divided into only two distinct regions. They are wingless, and without antennæ, and like the Crustacea are able to grow new limbs where others have been broken off.

There are three easily recognised orders of Arachnida, viz., (1) Scorpionidea (the scorpions), (II) Araneidea (the true spiders), and (III) Acaridea (the mites).

The differences between these three groups are such as to render the distinguishing of the various members fairly easy. Thus the scorpions are at once recognised by their large mandibles and segmented bodies, having a curved claw at the extremity; the spiders, by having the abdomen unsegmented and very distinctly separated from the anterior portion of the body, to which it is attached by a small thin stalk; the mites, by having the head, thorax, and abdomen appearing all in one piece.

The order Acaridea is divided into about eight families, the best known of which are the cheese-mites (Acarides), the Beetle-mites (Gamasides), the Plant-mites and "Red Spiders" (Trombidides), and the Giant-mites or Ticks (Ixodides).

The tick family has been divided into two very distinct divisions(1) Ixodes, the bush, cattle, and snake ticks; and (II) Argas, including the fowl and pigeon ticks.

To summarise briefly, we find that the ticks are gigantic mites related to the scorpions and spiders, and are modified insects belonging to the subkingdom of backboneless animals which possess jointed limbs.

Ticks.

The Ixodes are very different in form from the members of the genus Argas.

The argasids are flattish, having the mouth-parts upon the under surface of the body, and not visible from above; and in this feature and the habit of withdrawing their legs under their body they are somewhat tortoiselike. They also possess roughened skins.

The Ixodes have the mouth-parts terminal, situated at the edge of the body in the natural position of the head, the body is covered with a tough, smooth, leathery skin, which in the female is capable of a very great extension. An important character which separates these ticks from the argasids is the possession of a hard, horny shield upon the back behind the head.

The genus Ixodes has been divided into a number of sections, based upon anatomical differences of structure, and a separate genus Ophiodes has been erected for the reception of the snake-ticks; it has not, however, been considered necessary to enter into the consideration of these details here.

The mouth-parts of all ticks are constructed upon the same general principle. Taken together, they are called the rostrum, the most noticeable part of which is the proboscis or dart. This is a spatulate or pointed process of the labium or under lip of the tick, which is furnished beneath, and often along the sides, with recurved hooks, and forms the anchor by which the tick fixes to the skin of its host. The biting organs or mandibles are borne upon a pair of rods, which slide in and out upon the upper surface of the proboscis. These are covered or invested by a prolongation of the labrum, or upper lip.

On either side of the rostrum the palpi are situated. These are jointed organs, differing in shape and size in the various species. They are regarded as organs of touch, assisting in egg-laying, and when brought together they form a protecting sheath for the rostrum.

The rostrum and palpi are inserted into the front of a horny ring spoken of as the "mouth ring," which when comparing the tick to a bottle may be spoken of as the neck, and to the edge of which on the back is fixed the head shield.

When young, ticks have only six legs, but with age develop an extra pair. The first pair of legs bear near their apex sense organs, and they are used more as feelers than as locomotory organs, and are waved about in front when walking, after the manner in which an insect uses its antennæ.

The painful effects of a bite from ticks, upon man, horses, and dogs, are well known to all who live in the country, whilst even city people accustomed to spending their holidays at many of our pleasure resorts, are also acquainted with the irritation and severe pain often accompanied by swelling, which follow upon the attachment of a tick to one's skin.

Many of us, too, are equally aware that dogs are subject to the effects of "tick poison," and I myself have seen dogs go off time after time when their death could not be attributed to any cause other than ticks.

The paralysis or loss of the use of the hind legs is the most characteristic feature of an infested dog, and I have seen a dog die from ticks, although the ticks were removed before they had been attached more than two days. The nature of this effect produced upon dogs has not been fully inquired into, but that they do have such effects, and that dogs that having recovered from one attack seldom succumb to further attacks, but become, as it were, "tick-proof," I can fully testify.