The pathogenesis of H. contortus infection in lambs under 6 months of age challenged orally with 10,000 third stage infective larvae is described. The development of the parasite and its relationship to haematological and pathological changes are discussed, with particular reference to specific cellular mobilizations, and detailed descriptions are given of the haematology and parasitology, gross pathology and histopathology at 4, 7, 12, 18, 22 and 35 days after infection. Dramatic changes had developed by day 12.

Laboratory ferrets (Mustela putorius furo) were each inoculated with 500 larvae of a strain of Trichinella spiralis that had been passaged in mice for many generations. The recovery of adult worms from ferrets on Days 4 and 7 of infection represented a mean of 32% of the inoculum, with most of the worms being in the anterior three quarters of the small intestine. Larvae subsequently became encysted in the ferret musculature, with the diaphragm alone yielding as many as 5,750 larvae upon digestion.

For comparative purposes, mice were each inoculated with 200 T. spiralis from the same batch of larvae. The recovery of adult worms from mice represented a mean of 54% of the inoculum. An abrupt decline in worm population, typical of infections in the mouse, was observed in both mouse and ferret hosts; in neither species had the decline begun on Day 7 of infection, but it had clearly begun by Day 11 and was essentially ended by Day 14.

Liver histology and serum enzyme and protein changes were studied in two strains of mice showing different initial susceptibilities to infection with Mesocestoides corti. The results show an increase in ALT and AST levels during the period of invasion and proliferation in the liver and a decrease in the levels of these two enzymes following encapsulation of the parasite in the liver and liver regeneration. A progressive loss of albumin was accompanied by increases in the levels of the beta- and gamma-globulins. These changes are discussed in the light of our knowledge of the effects of this parasite upon its host.

The gross morphology and histological and cytological architecture of the lymph system of Orthocoelium scoliocoelium were studied. Each main vessel, near the intestinal bifurcation forms a spindle-shaped sinus. Lymphocytes, similar to the primitive blood cells, have been seen to form aggregates in certain regions of the lymph system. In addition, detailed histochemical observations were made on the localization and distribution pattern of various phosphatases, esterases and dehydrogenases. It is suggested that the lymph system, in addition to the functions already known, may also selectively reabsorb certain important outgoing higher fatty acids from the excretory system. Furthermore, the lymphocytes may also be involved in the defence mechanism of the worm. The nature and function of fine granules in the lymph remain speculative.

By transferring microfilariae of Brugia pahangi which had been born over a 24-hour period in the peritoneal cavities of jirds (Meriones unguiculatus) to the blood circulation of other jirds, infections of known age were tested for their ability to develop into third-stage larvae (L3) in mosquitoes Aedes aegypti. Microfilariae less than three days old were not able to develop to L3. Microfilariae which had been in circulation for three days to six months were capable of developing if ingested.

Infective larvae of Wuchereria, Brugia, Breinlia, Dirofilaria and Setaria species from an experimental vector, Aedes togoi, are compared. The distinctive bubble-like caudal papillae of Wuchereria bancrofti are readily distinguishable from the protuberant ones of Brugia spp; the ‘ear-like’ papillae of Breinlia are distinct from the ‘knob-like’ ones of Dirofilaria or the ‘thorn-like’ terminal papilla of Setaria.

Dentostomella kuntzi is redescribed from specimens found in the rodent hosts Acomys cahirinus, Arvicanthis niloticus and Rattus rattus from the Giza province of Egypt, and compared with three species of the genus Dentostomella namely D. grundmanni, D. legerae and D. translucida. Unlike other species in the genus, the egg of D. kuntzi is operculate. The distribution of adult D. kuntzi within the intestine of Acomys cahirinus is also discussed.