No significant difference was noted in canine hookworm infection due to hormone influence between the control group and the gonadectomized rats which were sacrificed 17 days after gonadectomy and 7 days after the infection. However in the rats which were infected 20 days after oophorectomy a significant difference was thought to be present in this group(176 +- 12.9 larvae/rat) compared with the control group (138 +- 21.2 larvae/rat). On the other hand, in the castrated group the number of larvae (138 +- 37.1 larvae/rat) was less than that in the control group (208 +- 43.4 larvae/rat). In the estrogen-injected male and female groups, there were no difference compared to the control, but the testosterone-injected groups of males and females showed more susceptibility to infection by A. caninum than in the control group. The Capillaria hepatica infection to the castracted host showed no significant difference between the gonadectomized and the control group. (oophorectomy; 214 +- 28.0), castration; 250 +- 36.5 and control; 191 +- 58.2 and 270 +- 30.1 adults/rat). Concerning the influence of the host's sex hormone on egg production of canine hookworm, there was a significantly decreased egg production in castrated dogs(6,578 +- 664.0 egg per gram) compared to the control dogs(9,711 +- 1,322.3 egg per gram). The same results were observed in vitro test. In the host, the susceptibility to hookworm infection was reduced in castrated rats, while oophorectomy group had a little or no effect. In the favorable or unfavorable hosts, testosterone gave the tendency of increasing susceptibility of the host to infection, while estrogen did a little or no effect.
