Notes on Diferences in Activity and Resistance between the Larvae of Ancylostoma duodenale and Necator americanus

Abstract

on the activity of these larvae and their resistance to adverse conditions, which indicate definite differences. Although the observations and experiments are of a preliminary nature, it seems worth while to publish them for the benefit of those working along similar lines, especially since it will not be possible for the author to continue work of this type. Table 1 gives the results of a series of experiments conducted in Soochow, China, in the summer of 1924 to test the resistance of infective hookworm larvae to drying. Small glass jars were filled with dry sand and the surface moistened to 2.5 cm. in depth. Hookworm larvae, consisting of a mixture of about 272 A. duodenale to 18 N. americanus, which had been cultured 14 days before and had been somewhat attenuated by vertical migration, were placed on the surface of these units, with about 290 larvae per unit. The units were then left to dry in a shaded place in the laboratory. Every third day three units were isolated and the larvae counted and identified.t As shown in Table 1, the larvae of Necator americanus were less resistant to drying, all of them having died before the ninth day, while Ancylostoma larvae were still obtained from the jars after 20 days, only the isolations on the 22nd day being negative. Necator larvae also appeared to be less resistant to formalin than those of A. duodenale. A drop of water containing 70 A. duodenale larvae and 14 Necator amncricanus larvae were mixed on a slide with one