For convenience of study, diseases are grouped according to the systems in which they cause disorder, as diseases of the respiratory system; of the digestive system; of the kidneys or genitourinary system; of metabolism; of the locomotor system, etc. Very interesting and important is that group of diseases which are incident to military service and the group of occupational diseases. (See DISEASES, OCCUPA TIONAL). The former includes °irritable heart," caused by forced marches in heavy marching order in those who are weakened by privation or illness, by dilatation of the heart, or by degenerated heart muscle. Syphilis, alco hol habit or tobacco favors its development. °Febrile exhaustion* is also seen in soldiers as a result of excess of acid in the muscles, and is characterized by remittent type of fever, weakness, nervous exhaustion and diarrhoea. °Feigned diseases' are especially trying to the regimental surgeon; for resort is not infre quently had to malingering to escape military duty and to enjoy the indolence of the hospital. Most frequently feigned are epilepsy, cholera, insanity, coma, blindness, deafness, heart dis ease and paralysis. The careful study of an experienced physician trained in neurology is often taxed to the utmost to uncover the fraud.
Diseases of occupation, or industrial dis eases, include bronchitis, emphysema, pneumo kiniosis, tuberculosis, lobar pneumonia, etc, among the respiratory disorders; cerebrospinal hyperamia, neuritis, fatigue neuroses, muscular atrophy, toxic paralyses and insanity, among the nerve disorders; eye diseases, from exces sive light or heat, or from dust, gases, burns or accidents; skin diseases (dermatoses) such as scalds, burns, eczema among flax-pickers; or the result of lead, arsenic and other poisons; heart and blood vessel disorders from lifting or other excessive strain; disturbances of the di gestive tract, as from poisoning with lead, arsenic, mercury, etc.; infectious disorders from pathogenic organisms in materials handled, including anthrax from hides and wool; gland ers; anchylostomiasis (hook worm disease), common among miners, etc.; caisson disease, common among those who work in compressed air, and due to the sudden transit to the ordi nary atmospheric pressure. Besides these, we have glass-blower's mouth, with swelling of the parotid gland. Women have increased suscep tibility to industrial poisons, such as lead, phos phorus or mercury, similarly as to tobacco. Much depends upon the individual resistance of the worker, his general health and strength, his place of work, its duration and the processes employed. The fatigue neuroses mentioned include writer's cramp, telegrapher's cramp, piano-player's paresis, etc., to all of which alco
hol habit, tobacco habit and mental anxiety pre dispose.
Climate has much to do with the prevalence of certain diseases. For example, cholera and yellow fever are found at sea-level in the tropics; malaria is found on either side of the equator, and is widespread; while sunstroke, mountain sickness and frost bite have been erroneously considered as due to climatic condi tions. All that one can truthfully say is that climate is predisposing.
We formerly encountered a classification including diseases,* founded largely on the false belief that sewer gas caused certain illnesses. These diseases were due to direct contamination, as by insects, or to dust, the conservator of germs.
Propagation of Disease.— The propagation of diseases by insects has been receiving in creased attention since 1894. Many mysterious, isolated causes of contagious diseases, as well as the progress of many epidemics, have been due to the facility with which certain disorders are transmitted by certain insects. The year 1894 is named because at that date Manson, of Dublin, appeared as a vigorous supporter of the theory that the mosquito was the cause of malaria. The theory had, indeed, been advanced by Crawford, an American physician, in 1807; again by Mott, of New Orleans, in 1848; and reasserted in 1883 by A. F. A. King, of Wash ington. Laveran, of Paris, who in 1880 discov ered the plasmodium malaria., advocated the theory in 1883. Through the studies and re searches of the Italians, Bignami, Bastianelli, Grassi and Celli, also Pfliigge, Pfeiffer and especially Manson, his pupil Daniels and Sur geon-Major Ross, of the British army, the dis covery was completed in 1898, that the an opheles mosquito is the carrier of malaria. Reed, Carroll, Agramonte and Lazear, ap pointed in 1900 an American medical commis sion to investigate yellow fever in Cuba, deter mined the fact that the Culex fasciatus mos quito is the host for yellow fever (q.v.). An other species of the Culex is the transmitter of filana. Elephantiasis has also been trans mitted by the mosquito. Still more culpable is the common house fly (q.v.) in the transmission of disease. It conveys to man the infection of bubonic plague, leprosy, anthrax, Asiatic chol era, typhoid fever, smallpox and diarrhcea. The flea that infests the rat is the common carrier to man of the virus of bubonic plague. The itch mite conveys leprosy. The tick propagates Texas fever among sheep. The ant has car ried bubonic plague as well as anthrax. The bedbug transmits leprosy, tuberculosis, cancer and relapsing fever, according to different ob servers. Roaches and house flies are carriers, not true intermediary hosts, of many disorders.