DISEASES OF THE RESPIRATORY ORGANS. 



31 



bryos to have been ingested and to have gained access to the 

 branches of the portal vein, they would then be carried to the 

 right side of the heart, and from thence to the lungs, by the 

 pulmonary artery, the capillaries of which ramify in the lung 

 substance alone, a situation in which the parasites did not 

 occur. To get to the bronchial mucous membrane they must 

 be returned by the pulmonary veins to the left side of the 

 heart, enter the aorta, and pass out by the small bronchial 

 arteries which supply the tubes — an exceedingly roundabout 

 and somewhat improbable route. It is to be remembered that 

 young strongyles have been found capable, like many other 

 nematoid worms, of reviving on the application of moisture 

 after a desiccation of a month or more, and even after immer- 

 sion in spirits of wine, and solutions of corrosive sublimate 

 and alum (Williams), so that their chance of survival under 

 adverse circumstances is unusually good. It seems quite as 

 reasonable to suppose that the dried embryos were inhaled 

 with the breath, and, lighting in the mucous membrane, found 

 suitable conditions for development. The position of the 

 parasites 'about the bifurcation of the trachea, at the angles of 

 division of the main bronchi, and most abundantly in the 

 lower wall of the tubes, just the localities where small particles 

 would be most likely to lodge, favors an infection through 

 the air rather than by the blood. ■ The negative evidences in 

 tlTe heart and blood-vessels do not go for much either way, as 

 the examination in all the cases was made after the invasion 

 of the parasites, and consequently at a time when they could 

 scarcely be found in the circulation. 



" It is a somewhat remarkable fact that verminous bron- 

 chitis prevails to a much greater extent, and is more, fatal in 

 young animals than in adults. Thus lambs and calves are the 

 chief victims in epidemics of ' hoose,' whereas it is only occa- 

 sionally that adult animals succumb to the disease. In lambs 

 the worms are usually found in the bronchial tubes, while in 

 sheep they are more commonly encysted in the lung tissue it- 

 self, where they do not appear to cause much irritation. It 



