The Natural History of Parasites. 
601 
One and the chief reason why the worm is so destructive to sheep 
and other animals, is the fact that the young worms are perfected 
within the part where the ova are deposited. Now, little hann, as a 
rule, will ai'ise unless the worms are present in large numbers ; but 
supposing one impregnated female only to inhabit a bronchial tube of 
an animal, that female would in process of time produce such myriads 
of worms that the animal must inevitably fall a sacrifice. 
The questions how the animals receive these worms, and how they 
come to occupy the ramifications of the bronchial tube, are difficult to 
answer. Although the worms are ovo-viviparous, and find their proper 
habitat within the bronchial tubes, nevertheless, ova ejected with any 
mucus that may be coughed up — and cough is a leading symptom of 
this disease — might remain as ova for an indefinite length of time 
upon pasture-land wathout losing their vital properties or power of de- 
velopment, and animals feeding upon the ground may receive the eggs in. 
the process of gathering their food, from which the young worms would 
be quickly produced. If an animal takes anything into its mouth with 
which there are a certain number of ova, imperceptible to the naked 
eye, these ova may be retained about the mouth with the mucus, or 
saliva, long enough for some of them to be hatched. Such worms 
would then find their way, not into the stomach, but into the bronchial 
tubes : the females would soon eject eggs, and the result would be a 
considerable brood of these creatures. Take the minutest portion of 
the ova-sac of a parent-worm, examine it thi'ough a good microscope, 
and such myriads of eggs will be seen on the field of vision that no 
one would think of attempting to count them. So that one worm, 
literally brings forth thousands of others. These, getting into the ra- 
mifications of the bronchial tubes, pass even to the air-cells of the lungs, 
where, by the irritation they create, they lead to condensation of the 
lung structure, and destroy the lung in these parts as an aerifying organ. 
The affected lambs fall off in condition, have a constant cough, and, 
gradually wasting away, ultimately become affected by diarrhoea, 
which usually carries them off. Many persons, upon observing their 
animals attacked with diarrhoea, attribute it to ordinary causes; 
whereas, it is in reality a general break-up of the system, depending, 
not upon a disease in the digestive organs, but upon the presence of 
these worms within the ramifications of the bronchial tubes. It is not 
at all an uncommon thing for 50, 60, or 70 per cent, of a flock of 
lambs to be destroyed from this cause. 
Remedies. 
The means at our disposal for getting rid of these entozoa consist 
of resistance to their attacks, and an endeavour, if possible, to destroy 
them where they ai-e, and thus effect their expulsion. These must be 
the principles to guide us whether we deal with worms as existing in 
the bronchial tubes, or any other part of the organism. When, how- 
ever, they exist in such numbers as to produce an organic change of 
the lungs, no kind of treatment can possibly avail ; early treatment 
before a change of the lung structure has come on, or the animal has 
