 However, he soon realized that gelatin, like potato slices, was not the optimal medium for bacterial growth, as it did not remain solid at 37 °C, the ideal temperature for growth of most human pathogens.As suggested to him by Walther and Fanny Hesse, Koch began to utilize agar to grow and isolate pure cultures, because this polysaccharide remains solid at 37 °C, is not degraded by most bacteria, and results in a transparent medium.During his time as government advisor, Koch published a report, in which he stated the importance of pure cultures in isolating disease-causing organisms and explained the necessary steps to obtain these cultures, methods which are summarized in Koch's four postulates.