Probiotics such as bifidobacteria are typically used in cases when a disease occurs or might occur due to a kill-off of normal bacteria. For example, treatment with antibiotics can destroy disease-causing bacteria, but also normal bacteria in the GI (gastrointestinal) and urinary tracts.
The 3-place Hiller Model 360, military H-23 Raven, was based on the U.S. Navy UH-12, which was first flown in 1948. The H-23 Raven performed as a utility, observation, and MedEvac helicopter during the Korean war.
The MiG-21 first came into service in the late 1950s and saw considerable service in the Vietnam War. The KPAF is estimated to be the fifth-largest air force in the world, with 110,000 service personnel and 820 combat aircraft. North Korean leader Kim Jong Un watches as a female fighter jet pilot performs drills. But there is considerable doubt as to how many of those aircraft, some of them dating back to the 1950s, are airworthy. Visitors to Pyongyang are often surprised by the sight of antiquated biplanes on the runway.