DISEASE. 291 DISEASES OF ANIMALS. xnersing in a mixture of absolute alcohol and ether. The preparation is stained to secure con- trast between the parasite and the blood-disks. l"nder the microscope, the plasmodicapi)earabout the size of re<l blood-corpuscles, discoid, star- shaped, in odd forms with prolongations, flagel- Ite and branches, nucleated, granular, etc. If DIPHTHERIA BACILLUS FBOM TRACHEA (X 500). not fixed, the parasites show rapid amoeboid movements in a fresh preparation. Other micro- organisms are described under the titles of the diseases they cause. Consult : Friedliinder, Mi- kroskopische Technik (Berlin, 1900); Thoma, l.ehrbuch der patlioloi/iscltcn Aitatomic. trans, by Bruce (London, 1896); Giinther. liakteriologie (Leipzig, 1898) ; Abbott, Principles of liacteriol- ofi!) (Philadelphia, 1898) ; Mallory and Wright, Pathological Technique (Philadephia, 1898) ; I-ehmann and Xeumann, Baktcriologische Diag- iiostik (Munich, 189G) : Steinberg. Bacteriology (Xew York, 1001): Park. Bacferioloi/y (New York and Pliiladelphia, 1900) : Bowhill. Bacteri- otoyii (Edinburgh, 1890); Fliigge, Die Mikro- organismcn (Leipzig. 1896). See Bactebia; MiCBOSCOPY; Malabia. DISEASES OF ANIMALS. In the gen- eral discussion of the diseases which affect animals, various systems of classification have been adopted by difTercnt writers. The scheme here presented is that most commonly adopted. Animal diseases may be grouped under the fol- lowing five heads: (1) infectious; (2) poisoning; (3) constitutional; (4) organic: and (.5) dis- eases caused by animal parasites. Infectious diseases are due to the action of minute organ- isms (bacteria) in the blood or vital organs and tissues. Such diseases may be coiunumicatcd from one animal to another bj' means of in- fected blood, by tissues, or by animal secretions containing the disease-producing organism. The most important infectious diseases of animals are abortion, actinomycosis, contagious agalactia, anthrax, asthenin. blackleg, braxy, cattle-plague, cerebrospinal meningitis, dog dis- temper, foof-and-raouth disease, fowl cholera, glanders, influenza, contagious pleuropneumonia, rabies, roup, swine-plajnie, tetanus. Texas fever, and tuberculosis. Each of these is discussed in n separate article. These diseases are due to the action of bacteria, with the exception of Texas fever, which is caused by an animal blood para- site, and rabies, of which the causative agent has not been determined. Under diseases of poisoning are included cases of poisoning of an acute or chronic nature by mineral, phmt, or animal poisons. The more common mineral poisons to which animals may gain access are compounds of arsenic, lead, cop- per, zinc, phospluirus and mercury, mineral acids, and caustic alkaline substances. Among plant poisons mention may be made of strjchnine, opium, aconite, and various wild plants, such as water-hemlock, larkspur, loco, veratrum, death- camass, and lupine. The eating of large quan- tities of ergot produces the symptoms of ergo- tism (q.v. ). Smuts and molds sometimes cause digestive disturbances of a more or less serious nature. Animal poisons include snake-poison, bee-stings, and the sting of certain other insects, such as the tselse-lly, bufl'alo gnat. etc. Diseases caused by animal parasites include those which are produced by parasitic worms, insects, mites, etc. Every species of domestic animals is infested to some extent with parasitic round or flat worms. The lung and stomach worms (q.v.) of sheep are periodically the cause of great losses to the sheep industry. The fluke- worm, which causes liver-rot (q.v.) of sheep and other animals, is of great economic importance. The nodular disease of fowls is due to the presence of tapeworms in the walls of the intestines. Trichinosis of hogs is due to in- festation by the round womi, trichina. Beef and pork measles are conditions produced by the presence of tapeworms in an immature condi- tion in the meat. The kidney-worm, which usually lies imiiedded in the fat tissue of hogs, occasionally penetrates the kidnev and causes death. Besides the examples al.cady given there is a considerable variety of round and flat worms which infest the intestines of domestic animals without causing'any marked disturbance except when present in unusually large numbers. Nearly all domestic animals are subject to mange or scab. This disease is due to the attacks of various species of mites. One species with several varieties causes one form of scab on sheep, cattle, horses, and goats. A few species of flies live, during a portion of their life cycle, as parasites on or in animals. Chief among these are the horse bot-fly. sheep bot-flv. or warble- fly, and horn-fly. The last tliree occasionally cause serious disease. Various species of ticks and fleas are well-known pests on domestic ani- mals. Under the head of constitutional diseases refer- ence is ordinarily made to such pathological conditions as anaemia, scur-y, and diabetes, which occasionally prevail in animals as well as in man. The term 'organic diseases' includes diseases of the skin, digestive' organs, respiratorv organs, circulatorv organs, nervous s.vstem, and urino- genit.al organs. Some of the numerous diseases which fall in this category are infectious. It will be understood that the system of classi- fication here proposed cannot be followed too strictlv, and that the different categories are not mutually exclusive. The various forms of scab and itch may readilv be transmitted from one animal to another by contact, and are, therefore, contagious. The terms infection and contagion, however, usually have reference to diseases which are due to the action of bacteria.
