The Relationship between the Intestinal Size of Young Mice and Their Susceptibility to Infection with the Cestode, Hymenolepis nana var. fraterna

Abstract

Several workers have noticed that very young mice are more resistant to infection with the cestode, H. nana var. frater,na, than are mice between two and three months of age. Woodland (1924) observed that the smallest and the largest mice are least liable to be infected naturally. Later, in controlled experiments, Shorb (1933) and Hunninen (1935) showed that considerably fewer worms develop in mice about one month old, than in those of the most susceptible age (about two and one-half months old). Although the differences are not as striking, the writer has recently noted this same relationship in a series of experiments involving young mice, most of which were 21 to 25 days old. The percentage development of cysticercoids in these mice was about six compared with about eight to ten in mice two and one-half months old. Of the suggestions offered to explain this difference, Hunninen's seems most plausible. In his opinion, the shortness of the intestine and the small size of the villi in the very young mice act as a mechanical disadvantage to the normal hatching and penetrating activities of the onchospheres. If this is really the reason for their greater resistance to infection with this tapeworm, any factor that would increase their intestinal size should make them more susceptible. It has been firmly established that the anterior pituitary of higher animals has a special relation to bodily growth and splanchnomegaly. The only figures that were found which showed a specific action of this gland on the development of intestinal tissue are from experiments with juvenile pigeons (Schooley et al., 1937) in which the response was accredited to the hormone, prolactin. By repeated injections of this hormone after hypophysectomy, the body of the pigeons was increased by eight per cent, intestinal length by 15 per cent, empty weight (weight after contents are removed) of intestine by 10 per cent, and villus length by 17 per cent over the corresponding values found in unoperated controls. It seemed desirable to test the effect of this hormone on the development of intestinal tissue in young mice to determine whether a similar increase could be produced, and, if produced, whether it would increase their susceptibility to the tapeworm.