VIRUS (Lat., poison, venom, slime). The term used in medicine to denote a palpable mor bid product causative of a contagious disease. If the contagious be fixed it is called a virus. If volatile. the term formerly used was the discovery of the hamatozo6n which causes malaria. the old term minsm has been restricted or abandoned. The term virus is still of any one of the infective agents which cause respectively typhus fever, relapsing fever. scarlet fever, smallpox, or measles. But it is confidently expected that a bacterium or protozo?M will be diseuvored to be the causative agent in each of these diseases.
Virus is also used as a synonym of lymph. in speaking of vaccine material. We also speak of the virus of syphilis, glanders. hydrophobia. etc., meaning the morbitie fluid which contains the germs of these diseases and is capable of propa gating them if inoculated into the human body.
In this way a culture of any bacteria may loosely be called a virus. The active principle of a virus has the tendency to reproduee itself after a period of variable length, called the period of incubation, which elapses between the time of exposure and inoculation and the day when symptoms of the disease are first noted. In measles the period of incubation is about ten days, though it may be protracted to thirty days; the virus being carried in blood from an ex anthematous patch or the secretion from the eyes or nostrils, and later from the scales that separate from the skin. In smallpox the period of incubation is about twelve days, though it varies from five days to three weeks. See BACTERIA DISEASE, GERM THEORY or.