Page:EB1911 - Volume 20.djvu/847

Rh Anopheles. Anopheles claviger (maculipennis) and Anopheles

bifurcates both are found in Great Britain; Anopheles pictus is

another species found in Europe, but so far not in

Species of Q^g^^ Britain. A member of the genus Culex, the

Mosquito ^ I f. . 1 . 1

Concerned, grey mosquito or Lulex jahgans, is the mtermcdiate host of the proteosoma of birds, on which many of the intermediate phases of the life-history of these parasites have been studied. Ross describes a dappled-wing mosquito as the one with which he performed his experiments on birds in India. Anopheles claviger is interesting in view of the former prevalence of malaria in Great Britain.

The remedy for malaria appears to be the removal or spoiling of the breeding grounds of the mosquito, thorough drainage of pools and puddles, or, where this cannot be easily effected, the throwing of a certain amount " of kerosene on the surface of these pools" (Nuttall).

Amoebic Dysentery. — In addition to the dysentery set up by bacteria, a form — amoebic dysentery or amoebic enteritis — has been described which is said to be due to an animal parasite, and it has been proposed to separate the various types of dysentery according to their aetiology, in which case the amoebic group is probably more specific than any other. The amoeba {.Amoeba dysenteriae, Entamoeba histolytica, of Schaudinn) supposed to give rise to this condition was first described by Losch in 1875. Since then this amoeba has been described either as a harmless parasite or as a cause of dysentery in Europe, Africa, the United States and in Brazil, and more recently in India. This organism, which is usually placed amongst the rhizopods, consists of a small rounded, ovoid or pear-shaped globule of protoplasm, varying in size frem 6 to 40/x, though, as Lalleur points out, these limits are seldom reached, the organism being usually from one and a half to three times the diameter of a leukocyte — from 12 to 26/i (see Plate II., fig. 19). Its margins are well defined, and the body appears to consist of a granular inner portion and a homogeneous outer portion, the latter being somewhat lighter in colour than the inner; in the resting stage this division cannot be made out. The organism appears to pass through at least two phases, one corresponding to a cystic, the other to an amoeboid, stage. In the latter stage, if the organism be examined on a warm stage, it is seen to send out processes, and, as in other amoebae, vacuoles may be seen as clear spaces lying in the granular and darker-coloured inner protoplasm. In the small vacuoles a deeply stained point may be seen. These vacuoles may be extruded through the ectoplasm. In some cases the vacuoles are so numerous that they occupy the whole of the space usually occupied by the granular protoplasm, and are merely surrounded by a zone of variable thickness, which " has the appearance of finely granular glass of a distinctly pale green tint" (Lafleur). In the cystic stage a nucleus which appears amongst the vacuoles may be made out, usually towards one side of the amoeba. This nucleus is of considerable size, i.e. nearly as large as a red blood corpuscle, and is readily distinguishable from the surrounding protoplasm. When stained by the Benda method (safranin and light green) a more deeply staining nucleolus may be seen in the nucleus. The nucleus is perhaps best seen when stained by this method, but it is always difficult to obtain well-stained specimens of this organism. If these amoebae can be kept under observation for some time evidence of amitotic division may sometimes be seen. Red blood corpuscles are often englobed by this amoeba, as are also micro cocci and bacilli. The movements of the amoebae are most active at a temperature of about 90° to 98° F. From the fact that pigment is contained in these organisms, it is supposed that they take in the red blood corpuscles as nutritive material, and that other substances may be taken in to serve a similar purpose. Nothing is known of the method of multiphcation of the amoeba., but it is supposed that it may be both by fission and by spore formation. These organisms are present in the early stage of the acute disease, and disappear at the later stages. Perhaps of some importance is the fact that the abscesses found in the liver and lung, which occur so frequently in cases of dysentery, usually contain, especially in the portions immediately adjoining the suppurating mass, a

considerable number of these amoebae. In the very small abscesses the amoebae are numerous and active, and occupy the capillaries in the tissues. It is quite possible that this plugging of the capillaries with amoebae is the cause both of the hemorrhage's and of the small areas of necrosed tissue, the supply of nutriment being cut off from the liver cells and from the lung tissues, and that suppuration occurs only as a secondary process, though Councilman and Lalleur maintain that the amoeba itself is the primary cause of suppuration. It is possible, of course, that the suppuration is due to the action of pus-forming organisms conveyed along with, or following, the amoeba, as we know that the growth of suppurating organisms can go on in dead tissues when these organisms have no chance of surviving in the healthy tissues and fluids of the body. Lafleur holds that the amoeba forms a toxic substance which exerts a direct devitalizing effect on the liver cells, and that the amoeba itself causes suppuration. The abscesses in the lung, which invariably extend directly from the liver and occur at the base of the right lung, also contain these amoebae. For these reasons this organism is looked upon as the cause of dysentery and of certain forms of dysenteric abscess.

They differ from the Entamoeba coli — often met with in the intestine — which has a more distinct nucleus containing larger chromatin masses and is surrounded by a highly refractive nuclear membrane. Further, in the Entamoeba coli the cytoplasm is of the same character throughout, there being no differentiation into ectoplasm and endoplasm. The Amoeba histolytica is often met with in a " resting phase, " in which the nucleus is less distinctly marked, and may consist of small masses of chromatin distributed throughout the cell or penetrating small buds formed on the surface. Around each of these buds, three, four or more, a highly refractive cyst wall is formed, the cysts becoming separated from the rest of the cell, the remnant of which undergoes disintegration. These cysts are extremely resistant, and probably maintain the continuity of the species outside the body.

In the active phase, the amoeboid form appears able by its tough membranous pseudopodia to push its way into the mucous membrane of the large intestine, especially the rectum, the lower part of the ileum and the flexures. Once it is ensconced in these tissues, small soft oedematous looking swellings soon appear on the mucous surface. Marshall points out that the amoebae probably reach the liver by the portal circulation from the dysenteric lesions in which the amoebae are found. Other observers maintain that the amoebae may pass through the walls of the intestine, through the peritoneal cavity, and so on to the liver where they give rise to typical abscesses.

Syphilis. — It has long been recognized that syphilis is a specific infective disease, but although characterized by fever, anaemia, and increased growths of tissue followed by rapid degeneration and ulceration of tissue, it is only within quite recent years that a definite parasitic organism, present in all cases of typical syphilis, has been isolated and studied. Schaudinn and Hoffmann, foUowed by Metchnikoff and others, have described as of constant occurrence a spiral or screw-shaped organism in which are seen from half a dozen to a dozen well-defined, short, regular, almost semicircular curves. This organism, when examined fresh, in normal or physiological salt solution, exhibits active screw-like movements as it rotates along its long axis; from time to time it becomes more or less bow shaped and then straightens out, the while moving about from point to point in the field of the microscope. It is not very strongly refractive, and can only be examined properly with the aid of special central illumination and in the presence of minute particles, by the movements of which the organism is more readily traced.

In order to obtain this organism for demonstration it is a good plan to wash the primary or secondary syphilitic sore thoroughly with alcohol; some of the clear fluid is then collected on a cover glass; or, perhaps better still, the lymphatic gland nearest to one of these sores may be punctured with a hypodermic needle, the fluid being driven out on to a slide on which some normal saline solution has been placed. When the organism has been examined alive the film may be carefully dried and then stained by Giemsa's