It is often of value to preserve the culture of a fungus for a long period of time. Such preservation not only furnishes the investigator with a permanent mount of the growth, but also allows the instructor to have access to cultures as life-like exhibits for use in demonstrating to his students.
Almost all present-day textbooks1 suggest that a formaldehyde solution be placed on the cotton stopper of the test tube, in order that the fumes of formaldehyde may kill the growth which has been placed within. The cotton stopper is then pressed slightly down into the tube, and the tube is sealed with paraffin wax.
This commonly used method invariably results in a quick cessation of the fungous growth, but fails as an effective preservative in that, after a few months, the formaldehyde is instrumental in destroying the color of the culture. Inasmuch as the color of the