Etiology. 103 



sufficiently considered; this predisposition, however, varies 

 consideiably according to species, age, nutrition; etc. Foreign 

 bodies which have penetrated into the lungs, likewise food aspi- 

 rated into the lungs of cattle, and also of other species of ani- 

 mals, ma}^ cause a croupous pneumonia ; this, however, depends 

 directly on the entrance of the foreign body and it does 

 not lead to a typical clinical picture of croupous pneumonia. 

 Some authors call all lobar processes croupous pneumonia, dis- 

 regarding entirely the fact that certain bronchopneumonias may 

 likewise assume the characteristics of a lobar process. 



The occurrence of a genuine croupous pneumonia as a 

 disease sui generis can therefore not be considered as an 

 estal)lislied fact. Croupous pneumonia of domestic animals 

 develops in consequence of the localization of some known 

 infectious disease in the lungs or in the course of a variety of 

 internal diseases. 



It has been a much contested question whether horses suffer 

 from any other genuine croupous pneumonia except influenza. 

 Several "authors (Roll, Friedberger & Frohner, Siedamgrotzky) 

 believe in the occurrence of a genuine croupous pneumonia 

 aside from influenza; the former, as a rule, occurs sporadically 

 in horses and in other species of animals and is usually not 

 contagious in nature. Other authors (Lustig, Sclmtz, Diecker- 

 lioff, Cadeac) include all croupous pneumonia in horses under 

 horse influenza. According to the view of the authors, so-called 

 genuine croupous pneumonia in horses not infrequently shows 

 such peculiarities in its appearance and course that the con- 

 clusion appears justified that these are simply cases of influenza 

 (see Vol. I). One can observe in all extensive epidemics of 

 influenza, that while a variable percentage of the horses of a 

 stable shows typical symptoms of influenza, others, even many 

 under the same conditions, suffer from a typical croupous 

 pneumonia. It has also lieen observed a number of times that 

 a horse, apparently suffering from a croupous pneumonia, may 

 have infected its neighbor, or even all of the horses of the 

 stable, with a disease which later on led to the typical picture 

 of influenza. It is indeed impossible to draw an exact line 

 between alleged genuine croupous pneumonia and influenza. 

 The occurrence of sporadic cases of influenza is likewise not 

 rare. 



Croupous pneumonia in horses is seen sometimes as the 

 sequel of external influences (cold, inunctions in skin diseases, 

 irritating vapors, smoke, exertions, tying the head high, throw- 

 ing for operations, contusion of the thorax). These were the 

 very cases which were cited as proof of the existence of a genu- 

 ine croupous pneumonia. It must, however, be claimed for the 

 majority of such cases that the nature of the disease is influenzal, 

 and that external factors, such as cold, which formerly used 

 to be considered as the exclusive cause of the disease are only 

 of importance as predisposing factors. These external in- 



