The Behaviour of sterilised exsheathed infective Trichostrongylid larvae in sterile media resembling their environment in Ovine hosts

Abstract

1. Attempts were made to cultivate in sterile artificial media the sterilised first parasitic larva of intestinal nematodes of sheep. These larvae were obtained by artificial production of the second ecdysis in 1 in 20 dilutions of Milton hypochlorite in distilled water. 2. Over 1,500 larvae were thus isolated, usually in hanging drops, in more than 200 different sterile media, containing ingredients likely to be present in the normal environment of these larvae inside their hosts. 3. None of the larvae showed any growth. Most formed the next sheath and were ready for the third ecdysis, but only 10 larvae actually performed this. The parasitic third larva thus liberated always emerged by a rent at the side of the eosophageal region of the sheath, and never by detachment of a cap like that characteristic of the second ecdysis. In every instance the parasitic third larva died immediately after the third ecdysis, which set it free. Two of these 10 larvae underwent the second and third ecdyses simultaneously. 4. The methods used by the writer (1933b) to induce artificially the second ecdysis always failed to produce the third ecdysis. No method of producing this at will was found. 5. The longest time any first parasitic larva lived was 41 days. Few of them lived, however, less than 8–10 days. A life of 18–30 days was more usual before visible signs of physiological abnormality appeared, such as the gradual vacuolation and emptying of the intestinal cells which usually preceded their death. 6. Those which were ready with a loose sheath for the third ecdysis, showed, as infective larvae also do, remarkable powers of resistance to changes produced in them by osmotic factors. 7. None of the larvae showed any particular reaction to blood, mucosa of the stomach or duodenum, nor, indeed, to any of the ferments or tissues these larvae encounter in their hosts. They seemed to be as indifferent in this respect as the sheathed infective larvae are. 8. A comparative physiological study of the sheathed infective and the exsheathed first parasitic phases of the second larva would verify, and perhaps modify, our knowledge of the functions of the so-called protective sheath of the infective larva.