During recent years various fungicides having a polyene structure have been isolated from streptomycetes. During the study of the action mechanism o f a new representative of this group, pimaricin. i t was established that the suppression of respiration of yeast by this substance was completely neutralised, if at the same time riboflavin and light were present. T h e cause of this phenomenon appears to be traceable back to a photodynamic destruct,ion of pimiracin under the .influence o f ri,boflavin.T h e effect is not restricted to riboflavin; some other colouring matters also possess this property. Ascorbic acid and hydmquinone repress 'the photodynamic reaction greatly. Arguments are presented for supposing that hydroxyl radicals are responsible for the annulment of ,the polyene group of the fungicide. So far ,hydrogen peroxide has been regarded as .the substance bringing about the photo-dynamic reactions.T h e screening programs for new antibiotics, whiich have been carried o u t on a very large scale, chiefly in industrial laboratories, have in the last few years brought to light fungicides from streptomycetes, which are ch'aracterised by a polyene structure. These substances possess characteristic absorption spectra. A short review o f this subject by Ball et al. 1) has appeared very recendy.A new representative of this group of fungicides ohas recently lbeen isolated and described under the name of pimaricin 2 ) . a colourless.reasonaibly stable sulbstance, melting with decomposition at -200O.An aqueous solution can be boi~led without loss of nctivity. Tqhe funlgicide in question has an absorption spectrum with cmaxi~ma at 279, 290, 303 and 318 m p in methanol and 281, 292. 305 and 320 m p in water. T h e combination of these maxima and their mutual intensities are typical for a tetraene structure such as is encountered in the 1)

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Establishing adequate resection margins during colorectal cancer surgery is challenging. Currently, in up to 30% of the cases the tumor is not completely removed, which emphasizes the lack of a real-time tissue discrimination tool that can assess resection margins up to multiple millimeters in depth. Therefore, we propose to combine spectral data from diffuse reflectance spectroscopy (DRS) with spatial information from ultrasound (US) imaging to evaluate multi-layered tissue structures. First, measurements with animal tissue were performed to evaluate the feasibility of the concept. The phantoms consisted of muscle and fat layers, with a varying top layer thickness of 0-10 mm. DRS spectra of 250 locations were obtained and corresponding US images were acquired. DRS features were extracted using the wavelet transform. US features were extracted based on the graph theory and first-order gradient. Using a regression analysis and combined DRS and US features, the top layer thickness was estimated with an error of up to 0.48 mm. The tissue types of the first and second layers were classified with accuracies of 0.95 and 0.99 respectively, using a support vector machine model.