POULTRY DISEASES 
27 
CHICKEN POX 
CAUSES.—This disease is called contagious epithelioma. It affects 
chickens, turkeys, pigeons and geese. Some investigators claim it is due to 
an ultramicroscopic germ, and that the germ is also the cause of avian diph¬ 
theria or roup. An ultramicroscopic germ is one that will pass the pores of 
the finest filters and which cannot be seen with the microscope nor grown 
in visible quantities upon culture media. There are just as many who are 
certain that their results show that the germs are not the same, and that the 
infection at one time will not produce roup and at another chicken pox. Our 
experiments do not lead us to the conclusion that they are the same disease 
caused by the same germ. 
Chicken pox is contagious and can be transmitted from material of one 
bird to healthy birds by inoculation. Several germs have from time to time 
been isolated, among them protozoa, but none are constantly present in these 
cases. 
Fig. 26. 
Figure 26.—Chicken pox (contagious epithelioma) slightly reduced; a, some 
well formed pock nodules consisting of masses of proliferated epithelium. It will 
be noted that some of these have obstructed the eye; b, shows some nodules at 
the base of the beak. This condition is sometimes found accompanying roup. 
SYMPTOMS.—Figure 2 6 shows a photograph in which nodules of ir¬ 
regular size are seen over the comb, face and in the wattles. These nodules 
vary in size up to a pea and even larger. We have observed roup and chicken 
pox in the same flock. 
ROUP OR AVIAN DIPHTHERIA 
This condition is sometimes called swelled head, because usually there 
is swelling about the head. 
CAUSE.—The cause appears to be far from settled. American and 
European investigators have from time to time isolated different germs, all 
of which perhaps contributed to the production of conditions found, but there 
