Filtered.
1⁄2% carbolic acid added. Let stand.
Filtered (porcelain filter).
Old Tuberculin contains:
1. 40 to 50% glycerine (a small percentage of glycerine is evaporated)
2. 10% of peptones or albumoses
3. Toxic secretions of the tubercle bacilli into the culture fluid, or such of them as are soluble in 50% glycerine
4. Substances extracted from the bacterial bodies by the alkaline broth during the process of boiling and evaporation.
Appearance and Characteristics:
1. A clear brown fluid