THE EESPIRATOEY APPAEATUS. 319 



Asthma consists in inflammation of the muscular coat 

 of the bronchial tubes, which atrophies, whereby either 

 dilatation of the tubes occurs, or, since due supply of 

 air to each air-cell is not regulated, these become dilated, 

 and eventually ruptured, so that air escapes into the 

 interlobular areolar tissue. The latter condition is known 

 as interlobular emphysema ; the former is vesicular emphy- 

 sema. Dilatation of an air-cell leads to impervious con- 

 dition of the beautiful capillary network on its walls, 

 and so atrophy of the affected part of the lung is pro- 

 duced. The conditions observed in addition to these in 

 scrofulous bronchitis have been already denoted. We 

 can do nothing to cure these states, and but little to pal- 

 liate them. Stimulant tonics, easily digestible food, and 

 quiescence, will keep the animal alive for some time, 

 but the owner will generally prefer destruction of the 

 patient. 



Parasitical Bronchitis, "hush/' " hoose," or "hoast-/' 

 phthisis pulmonalis verminalis. — This disease is of frequent 

 occurrence among calves under a year old ; it certainly is 

 seen in older animals when they are in a debilitated con- 

 dition, but seldom proves fatal in such cases, though it 

 sometimes causes considerable mortality among calves, for 

 in them there is not sufficient constitutional stamina to 

 enable them to resist the debilitating effects of the para- 

 sites. In the older animal the parasites may be found in 

 numbers in the lungs, even when no special indications of 

 their presence have been given ; but it must be clearly 

 understood that their ill effects are directly proportional 

 to the strength of constitution of the patient and the 

 number of the parasites. These worms are known as 

 8trongylus micrurus, the same parasite as is found so fre- 

 quently in the lungs of the ass. They are armed nema- 

 todes, and are also found sometimes in the alimentary 

 canal, and Williams notes their presence in the heart and 

 blood-vessels in some cases. Hence it is inferred that 

 they arrive at the lungs by entry of the alimentary canal 

 with the food, boring a passage into the blood-vessels, 

 passing with the current of blood through the blood- 



