236 Enzootic I'neumoiiia of Young Aiiinials. 



of cases, to a certain species, so that only the young of the same species 

 are susceptible to contagion. If, however, its virulency becomes in- 

 creased, or if certain environmental conditions become favorable to 

 microorganisms, it may spread to young animals of another species, and 

 exceptionally to adult animals of this kind. (Pr. Vb., 1905, ii, 17.) 

 Young animals may also be infected from adults, as occurs in hem- 

 orrhagic septicemia of cattle, in swine plague and in hemorrhagic sep- 

 ticemia of sheep. 



The same general rule might apply to pneumonia of the young 

 caused by other microorganisms, but observations proving this are still 

 lacking. 



The etiology of enzootic pneumonia of sucking foals has not yet 

 been investigated ; but the occurrence of this disease appears to be very 

 probably due to some of the bacteria mentioned above. (Kutzbach 

 observed an enzootic bronchopneumonia similar to that of calves among 

 foals which had had an attack of strangles a few weeks previously.) 



Natural infection occurs by sucking an unclean udder, 

 through contact with straw, by licking the walls, through inges- 

 tion of infected food, through inhalation of droplets of secre- 

 tion, which are coughed up by sick animals, through the stump of 

 the umbilical cord, through abrasions of the skin. Sick animals 

 confined to a stable will spread the infection by expectorated 

 bronchial secretion, by intestinal discharges which may contam- 

 inate the floor, the straw, the feed remnants, the crib, and which 

 may remain virulent upon the infected objects for a long time. 

 The disease has, therefore, a tendency to become stationary in 

 localities which have once become infected, unless prophylactic 

 measures are carried ont. Intrauterine infection, as claimed 

 by Galtier, has not been proved to occur. The importation of 

 the disease into hitherto free herds is usually brought about by 

 young or adult animals which have passed through the disease, 

 yet have not fully recovered. The disease is not rarely spread 

 to new localities by obviously sick animals or by the attendants. 

 1+ is spread most easily by sick animals of the same species. 



The disease may make its appearance among animals which 

 were heretofore free from the infection without importation 

 from outside. If this occurs it must be assumed that the causa- 

 tive microorganisms have been present as saprophytes and have 

 for some reason acquired pathogenic properties or that the 

 power of resistance of the sucklings has for some reason been 

 diminished by external influences (breeding of thoroughbred 

 stock). 



External influences, such as cold, sojourn in cold, drafty, 

 poorly ventilated stables, favor the spread of the disease or 

 cause a more virulent course. Another predisposing cause is 

 primary intestinal catarrh or diarrhea (Poels) and too much in- 

 breeding. 



Pathogenesis. Some of the pathogenic bacteria mentioned 

 above, especiall,y bacillus bipolaris, mnlti])ly, in certain cases, 

 very rapidly in the blood of the infected animals, and thus pro- 

 duce septicemia. If the latter does not lead to death in a short 



