The present invention provides methods for identifying new compositions having one or more desired activities, and methods for identifying organisms that are sensitive or resistant to a drug composition. Light of selected wavelengths is passed through blood or body tissue and the transmitted or reflected light is detected and the detected signals can be electronically compared and manipulated to provide the non-invasive, continuous and quantitative display of a patient’s blood urea, blood osmolarity, plasma free hemoglobin and tissue water content. The preservation process has a relatively short process time, wherein a good preservation is realized while the mechanical strength of the wood is largely retained. Another embodiment involves use of a self-expandable mesh to expand the surrounding prosthesis and secure it to the vessel wall.