The effect of low temperatures on nematodes of sheep

Using micro-freezing apparatus devised for the purpose, the author has studied the effects of cold on the infective larvae of Nematodirus sp.. Chabertia ovina and Oesophagostomum columbianum. The latter lives for not more than eight weeks under conditions simulating those of an Eastern Canadian winter; the former survive for at least 18 and 16 weeks respectively and so are able to overwinter and infect lambs in the spring. Quick-freezing (i. e. a sudden temperature drop to -4°F. or -38°F. ) is quickly lethal for all species studied as a result of intracellular lesions induced by the sudden change. The hypothesis is advanced that the sudden drop in temperature causes the protoplasmic sol to change to a gel which breaks up into globule-like structures (possibly fats or proteins). This process produces changes in intracellular osmotic pressure, resulting in rupture of the intestinal cell membrane. The changes are illustrated by camera lucida drawings and photomicrographs.