The eggs and rhabditoid larvae of canine hookworm were irradiated with ultraviolet rays for one hour at a distance of 10, 20, 30, and 40 cm. The infective stage larvae of the same parasites were irradiated for l, 3, 5 and 14 hours from the same distances. The infective larvae were also exposed under direct sunlight for l, 2, 3 and 4 hours.

Parasites…Ancylostoma caninum was used. Eggs were collected in vitro from female adult worms. The worms were kept at 37℃ in petri-dish filled with Kreb's Ringer solution. There was an average of two cell stages, and they were used as early as possible before the morula stage.

Rhabditoid larvae were obtained by culture of the above eggs for twenty-four hours in 25℃ incubator. The larvae reached the infective stage in seven days culture at the same condition.

Irradiation of Ultraviolet Ray…Kingston ultraviolet light (100 volt, 10 watt, 50 cycles, 0.230 ampere) was used. The potential U.V.R. power was 1.8 watts. The distances between the material and the light were 10, 20, 30 and 40 cm at a temperature of 25℃ in each case. The samples were smeared on the tile in order to keep them in saturated moisture. Fully wetted ten ply gauze was laid underneath the tile. The tile was surrounded by 2×5 cm rectangular piece of glass in order to prevent the spread of the larvae to the outside.

All of the samples received irradiation for one hour and were cultured for a period of seven days. The hatching of the egg and the development of the larvae were observed. For the purpose of the study, the infectivity and pathogenicity of the irradiated samples, were inoculated into mice orally. The lungs, livers and carcass were examined three days after the infection.

A routine pathological examination of the organs was also carried out. In order to study the eggs productivity, the larvae were given to the proper host, dog. The eggs in the feces were examined from three to 6 weeks after infection, both quantitatively and qualitatively.

As a supplementary experiment, the infective larvae of canine hookworm were exposed four hours under direct sunlight (September 25), and the infectivity and pathogenicity of the host were examined.

Hatching, development and infectivity of irradiated eggs: Hatchability of the irradiated group for one hour according to the distance from the light to the sample were 48.0% at 10 cm, 60.3% at 20 cm, 85.2% at 30 cm and 88. 2% at 40 cm respectively. None of them developed to the infective stage. They remained rhabitoid for several days and were destroyed. None was found alive in the host. 93.0% of the control group hatched and developed to the infective stage.

Development and infectivity of irradiated rhabditoid larvae: None of the irradiated group reached the infective stage. Under irradiation they coiled and died soon after straightening out again. Only the group irradiated at the distance of 40cm survived for six days. They finally granulated. There was no manifestion of irradiated larvae alive in the host tissue.

Life span, infectivity, pathogenicity and egg-productivity of the irradiated infectve stage larvae: All were destroyed in the group of fourteen hours irradiation at 40 cm distance. Thirteen precent survived in the five hours irradiation group at the same distance. The survivability of larvae was reduced by the period of irradiation and at the shortest distance. The infectivity to mice was only 0.8% at 30 cm, and 8.2% at 40 cm in the three hour irradiation group. The recovery of the infected larvae from the host tissues was reduced as the irradiation period was increased and the distance shortened. The pathogenicity was paralleled with the vitality of the irradiated larvae.

From the groups of one hour irradiation and ten cm distance, three hour irradiation and ten to thirty cm distance, the egg-productivity was all negative. But as the irradiation period decreased and the distance lengthened the egg-productivity tended closer to normal. The infective stage larvae which were exposed to direct sunlight were destroyed within three hours, but survived 81% in the one hour exposure group and 20% in the two hour exposure group.

The summary of the results is as follows:

1. The hatching of eggs was reduced to half for one hour irradiation at the ten cm distance. Even hatched larvae did not develop to infective stage.

2. Infectivity was inhibited by the irradiation to at the ten cm distance for one hour. About ten% of the irradiated infective stage larvae were recovered from the infected animal among the group of 40 cm distance for one hour.

The egg productivity became lower in the group of one hour irradiation at 40 cm distance.

3. The pathogenicity of the irradiated group was mild compared to the control group.

4. The direct sunlight destroyed the infective stage larvae within three hours.

In general, the ultraviolet ray showed the inhibitory action in the hatching, development, pathogenicity and egg-productivity of the hookworm.

The grade was paralleled with the period of irradiation and reversed to the distance between the light and samples.