This study was carried out in order to find out the valuable measure to kill the parasite eggs in night soil.

The fresh eggs of Ascaris put into human stool were irradiated with Cobalt 60 of 200,000 to 1,000,000 rad and cultured in test tubes at 25-30℃, washing with 2% formalin solution every 24 hours. The continuous development of those eggs were observed under microscope and the proprotions of developed eggs were compared with those of control groups.

The major result can be summarized as follows:

1. In general, The eggs in stool developed poorly than the eggs in saline.

2. If the eggs were irradiated with the larger dose of Cobalt 60, the proportion of developed eggs were reduced subsequently.

3. The eggs irradiated with the dose of 1,000,000 rad in saline developed in the proportion of 15.5%, whereas irradiated with 200,000 rad 94% developed in 4 weeks.

4. The 44.5% of eggs in stool irradiated with 200,000 rad developed after 4 weeks, 30.5% with 300,000 rad, 25% with 500,000 rad and 3.5% with 1,000,000 rad respectively.

5. The effective minimum dose of Cobalt 60 irradiation to kill the Ascaris eggs in stool was estimated 1,000,000 rad.

Further examination will be required to observe the infectivity of irradiated Ascaris eggs to animals and to evaluate the effect from the standpoint of sanitary engineerings.