An improved method of preparing nisin.

1. Weights and ,-glucuronidase activity have been determined in lymphatic organs ofrats (lymph nodes of the neck, thymus and spleen) from 4 hr. to 15 days after total-body irradiation (200, 400 and 600 r.). 2. The activity of the enzyme increased in the first period after the irradiation (from 4 hr. to 5 days) when the tissues underwent a rapid decrease in weight. Histological examination showed then extensive pycnoses of lymphocytes, fragmentation of cells and phagocytosis. In the second period, in which reconstitution of the tissues took place, the behaviour of the enzyme activity was variable, depending on the organ and on the dose of radiation administered. 3. After X-ray irradiation the positive correlation between increase of P-glucuronidase activity and atrophy of the tissues, already found in the atrophy of lymphatic tissues caused by fasting, was confirmed. 4. The increase in fl-glucuronidase activity observed should be considered as a secondary effect of the irradiation, as it can be reproduced by different experimental conditions such as fasting.