THE PRINCIPLE OF IMMERSION MICROREFRACTOMETRY FOR THE DIRECT DETERMINATION OF LIVING AND DEAD BACTERIAL CELLS
ARMY BIOLOGICAL LABS FREDERICK MD
Pagination or Media Count:
The determination of the number of living and dead cells and their quantitative relationship in microbial populations or suspensions has great significance for the various fields of practical and experimental microbiology. In spite of the large number of methods proposed cultural, morphological, chemical, cytochemical, up until the present time microbiological technique does not have available a sufficiently accurate, objective and simple method for the direct differentiated calculation of living and dead bacterial cells. This is explained by the fact that the methods used at the present time, regardless of the principle they are based on, do not make it possible directly, without additional effects and with a sufficient authenticity, to ascertain the setting in of death of the bacterial cell. In connection with this, attention is merited by the phenomenon of the irreversible changing of the optical properties increase of optical density and light refractive index of the cells as a result of their death. A sufficiently sharp exposure and quantitative evaluation of the stated phenomenon became possible only after the introduction of microscopic investigation by the phase-contrast method. An important improvement of the method was the use of special immersion media. The use of exact concentration of albumin solutions made it possible to develop a microrefractometric method for determining the concentration of dry substances and water in living cells.