In order to know the sterilization efficacy of ultraviolet irradiation on microbial aerosols, the size and the weight of the aerosol particles were evaluated, and these were irradiated under dynamic air flow created by an experimental air conditioning system. The experimental apparatus consisted of a high efficiency particulate air (HEPA) filter, an aerosol generator, spiral UV lamps placed around a quart glass tube, an Andersen air sampler and a vacuum pump. They were connected serially by stainless steel ducts (85mm in diameter, 8m in length). Six types of microbial aerosols generated from an ultrasonic nebulizer were irradiated by UV rays (wavelength 254nm, mean density 9400 µ,W/cm2). Their irradiation time ranged from 1.0 to 0.0625 seconds. The microbial aerosols were collected onto the trypticase soy agar (TSA) medium in the Andersen air sampler. After incubation, the number of colony forming units (CFU) were counted, and converted to particle counts.
The diameter of microbial ae1osol particles calculated by their log normal distribution were found to match the diameter of a single bacteria cell measured by a microscope. The sterilization efficacy of UV in standard airflow conditions (0.5 sec. irradiation) were found to be over 99.5% in Staphylococcus aureus, Staphylococcus epidermidis, Serratia marcescens, Bacillus subtilis (vegetative cell) and Bacillus subtilis (spore) and 67% in Aspergillus niger （conidium). In A niger, which was the most resistant microbe to UV irradiation, the efficacy rose up to 79% when irradiated for 1.0 sec., and it was observed that the growth speed of the colonies was slower than that of the controls. It was thought that UV rays caused some damage to the proliferation of A niger cells.
The previous study showed that an unusual mineralized tissue appeared in the bone marrow of rats 5 days after colchicine injection. The bone marrow stroma cells isolated from the colchicine treated rats were cultured and characterized to elucidate the relationship between the bone marrow stroma cells and the unusual mineralized tissue. The bone marrow cells were obtained 1 to 5 days after the injection of colchicine and the attached cells (marrow stroma cells) were cultured and tested for alkaline phosphatase (ALP) activity as a marker of osteoblastic characteristics. The cultured cells isolated 2 days after the injection (Col. 2 cells) showed a low ALP activity during the initial culture period. However, the activity began to increase and showed a high level from the 14th to the 30th day of culture. The other cell populations did not show an increase of ALP activity during the culture period. The ALP of the Col. 2 cells resembled the bone type enzyme by their biochemical characteristics. The Col. 2 cells became to respond to both the parathyroid hormone and prostaglandin E2 during the late stage of culture period. These findings suggest that the bone marrow stroma cells isolated from the rats 2 days after the colchicine injection become enriched with osteoblast precursor cells. These cells might differentiate into the osteoblasts during the repair process following the severe damage after the colchicine injection and produce an unusual mineralized tissue in the bone marrow cavity.