and by the absence of any finely granulated appearance. Those most important to name in this place are,

Bacterium carbunculare, said to be found in the blood of men and animals who have died with carbuncle. Defined as "motionless, flat, straight, highly refractile, without inflexion when short, and with one or two inflexions when long."

"Bacterium catenula (chain-like), a doubtful species, supposed to have been found in typhoid fever.

"Bacterium cuneatum (wedge-shaped), said to exist in putrefying blood, and in the intestines of horses and dogs dying of putrefactive diseases.

"Bacterium termo, described as two to five times as long as broad, about .0015 mm. in length; often two-jointed, with a vacillating movement, produced by a terminal flagellum. Found wherever putrefaction of either animal or vegetable matter is going on, and believed, by many, to be the active agent in that process. When putrefaction ceases they cease to be found."

Bacillus.

of

Meaning a little stick. (Power and Sedgwick.) A genus the tribe Desmobacteria of the family Bacteriaceae. Distinguished from the other genus of the same tribe, Vibrio, by the straightness of the rods.

"Bacillus anthracis. Homogeneous and unjointed when fresh, and developing spores. It is found in the blood and diseased structures in the splenic fever of animals, and in malignant pustule.

"Bacillus lepra. A form of uncertain existence, supposed to be the cause of leprosy.

"Bacillus malaria. A form discovered by Krebs and Tommasi-Crudeli in the air and soil of malarious districts, especially in the Pontine Marshes, and believed by them to be the cause of intermittents. It consists of small, narrow, longish cylindrical spores, about half a micro-millimetre long, and rods of about the same breadth, and seven micro-millimetres in length. In the body of animals the spores develop into long filaments, which subsequently undergo transverse segmentation, so as to form a chain, in the segments of which new spores grow. They develop most freely in the spleen and the medulla of the bones."

Spirillum.

In addition to the divisions named above must be added the Spirillum, a parasite of the class algæ, and coming also under the head Bacteria. Spirillum is ranged by Dr. Vandyke Carter amongst "Bacteria (Schizophyta), forming (like Bacillus) a member of the Nematogenous subsection, in which the component cells are arranged in rows, and come into a small group characterized by colorless, screw-shaped threads embracing three genera :Vibrio, in which the filaments are short and slightly undulating; Spirillum, in which they are short, spiral, and stiff; and Spirochate, in which they are long, spiral, and flexible."

Bacillus Tuberculosis.

A Bacillus supposed to be found in the sputa or expectoration of persons suffering from some forms of consumption, and in the walls and contents of tubercular cavities. The parasites, rendered visible by a process of double coloration, and usually demonstrated colored with methyline blue, are seen as minute rods about the third of a diameter of a blood corpuscle in length, and about onesixth of their own length in breadth. In some of them spores are said to be evidenced, but in the specimens I have seen none were manifest.

CHAPTER VII.

ON PARASITES AS CAUSES OF DISEASE.

THE reader who has studied carefully the history of disease in the part of this work devoted to the description of local diseases of natural origin, will easily have connected many of the parasites described in the last chapter with the diseases in which they have been found, and will to a considerable extent have learned the part they play as factors of disease.

It will, however, be advisable to consider this subject a little further on, in order to understand how far the presence of a parasite growth may be taken as a first or second cause of the phenomena of disease in the cases of disease in which the growth is discovered.

In this review it will, I think, be most convenient to follow out the exposition by a reference to the parasites under the three great divisions in which they are described at the opening of the last chapter, namely, as:

Entozoa, or Worms.

Ectozoa, or Acari.

Entophyta and Epiphyta, or Algæ, or Fungi.

DISEASES FROM THE ENTOzoa.

There are three kinds of the Entozoa, or worms, which affect

the body as parasites.

1. The Nematode, or round worms.

2. The Cestode, or tape worms.

3. The Trematode, or fluke worms.

NEMATODE DISEASE.

The Nematode or round worms include the Trichina spiralis; the Ascaris lumbricoides or common round intestinal worm; the

Oxyuris vermicularis or thread worm; the Dracunculus medinensis or Guinea worm; and the Filaria sanguinus hominis.

Trichiniasis.

The trichinous flesh-worm disease,-Trichiniasis, has assumed in some countries the character of an epidemic, but in England we have learned its history, chiefly, from isolated examples of it. In order that the disease may be induced the trichinous parasite must enter the body by the alimentary canal. The human subject derives the larval trichinæ from the muscular flesh of some animal on which he has fed. The parasite as it exists in this flesh is in the larval state, the state intermediate between the eggs and the perfectly developed growth,—and in this condition it remains so long as it is embedded in the flesh. Received into the stomach of a man, or of any other animal, it develops into maturity in a few day. The female trichinæ give forth their embryos in abundance, and the embryos at once make their migrations through the cellular connecting network which holds all the active and muscular organs of the body in close connection.

In this country, disease from the presence of trichinæ in the tissues is very rare, and few English physicians have had opportunities of studying it. I have seen one portion only of a trichinous muscle derived from man, and in that case the existence of the parasite was not detected prior to death. On the continent there have been epidemics of Trichiniasis, attended, in extreme instances, with intense symptoms.

When the trichinous disease occurs it is marked in its most developed form by three stages. (a) A stage of intestinal irritation, gastro-enteric,-corresponding with the period of full development of the trichinæ, and the evolution of embryos within the canal. (b) A stage of moderate fever, attended with pains in the muscles like those of rheumatism, and accompanied, in some few examples, with a red rash, and boils,-corresponding with the time when the embryos find their entrance into the muscles and are becoming encysted there. (c) A prolonged or chronic stage of impaired muscular movement with emaciation,-corresponding with the after-period when the larvae are entirely encysted in the muscle and are fixed in position. This last stage is not always well marked.

When the first or acute affection is over, and the parasite is duly lodged in its home, it happens, usually, that the evidence of the disease gradually ceases, and that the presence of the foreign intruder is not, actually, discovered until after the death of the person into whose organism it has intruded. Such was the state of the body which presented the one single instance I have known of trichinous affection.

The trichinous parasite in its larval condition enters the body, as we have seen, with infested animal food. There is no satisfactory evidence, however, that it ever becomes active when it enters after the food it infests has been subjected to perfect cooking and to the temperature of boiling water. This degree of heat, 212° Fahr., destroys quickly and completely the life of the embryo. The worst cases of disease have been those in which the sufferers have swallowed raw or imperfectly cooked infested flesh.

Nevertheless, the larvæ enjoy a tenacious life; they exist ready for development into the mature state even when the flesh in which they are encysted has passed into decomposition. The flesh of the pig is the most frequent carrier of the trichinous larvæ.

Lumbricoid Disease.

Other nematode worms, two of which are well known, produce symptoms of disease in the human subject. The large round worm, the Ascaris lumbricoides, is one of these common parasites. It attains often a considerable size, resembling in its appearance the ordinary earthworm. It is developed and retained in the intestinal canal, and creates, frequently, extreme irritation, leading to convulsions and comatose sleep in children, and to that emaciation which almost invariably occurs when a body foreign to the alimentary surfaces is long in contact with them.

Thread-worm Disease.

The small round worm, known as the thread or wire worm, Oxyuris vermicularis, is another parasite which infests the lower part of the alimentary canal, and in children is a frequent source of extreme irritation. As a rule it infests children only, but the rule is not without its exceptions. For a long time I had under observation a middle-aged man who, throughout his life, has recurrently been tormented by this parasite. The symptoms it