Etiology. Pathog-eiiieity. 291 



Tenacity. Blood placed in glafs tubes, the ends of which were closed by 

 melting, and kept in a dark place, retained its virulence for three months, while 

 the filtrate was virulent for only one week. Heating to 55° destroys the virus 

 within a half hour, at G0° in 5 nunutes, at 65° immediately (Centanni). According 

 to Maue the vii-us remains active in dried spinal cord, or liver substance, for 200 

 days, in blood mixed with glycerin (aa) for 270 days. According to Ostertag & 

 Bugge it is destroyed by drying in a thin layer, or by putrefaction after 39 days; 

 on being subjected to a temperature of 70° it is killed instantly. A 1% corrosive 

 sublimate solution destroys it in 30, a 1% sulphuric acid and a 3% chlorate of lime 

 solution in 10 minutes (Lode). A hot 2% soda solution, as well as a hot 5% creolin 

 solution are also effective (Ostertag & Bugge). 



Pathogenicity. Chickens and turkeys, pheasants, sparrows, 

 black-birds, sparrow-hawks, owls and parrots are susceptible to 

 the virus, while water fowls and pigeons as a rule resist the 

 natural, and frequently also the artificial infection; mammalia 

 are not at all susceptible. 



Old geese can be infected only by subdural inoculations, those 

 only half a year old however by subcutaneous or intramuscular inocula- 

 tions, as well as per os. In these birds the disease manifests itself 

 principally in nervous symptoms (see symptoms). Lode & Gruber 

 and Centanni succeeded in infecting pigeons only by repeated injections 

 of large quantities of virus, Maggiore & Valenti only after previous 

 starvation with blood injections ; Freese however produced the disease in 

 them by letting them live with chickens. Successful infections in ducks 

 are reported by Leclainche, and spontaneous infection of a parrot by 

 Stazzi. 



The natural infection is probalily transmitted mostly by the droppings and 

 the nasal secretion of affected birds, and also by the blood of killed animals and by 

 the organs of those dead from the disease, which are ingested with the food by 

 healthy chickens (by feeding such material the disease has been produced arti- 

 ficially). Occasionally the virus may enter the bo<ly through injuries of the skin; 

 at least it was found that the disease may be pro<luced artificially very easily and 

 positively in this manner (it is sufficient to dip the needle of a syringe into infected 

 blood, and slightly scarify the skin with it; Kleine & Mollers succeeded in pro- 

 ducing the disease by droi)ping the virus into the conjunctival sac). 



Parasites living on affected fowls (Dermanyssus avium) cannot 

 transmit the disease, and it cannot be even produced by subcutaneous 

 injections of such macerated parasites (Centanni). 



Anatomical Changes. In very acute cases the autopsy 

 sometimes reveals negative findings, or frequently only punc- 

 tiform hemorrhages on the inner surface of the breast bone, on 

 the visceral layer of the pericardium, on the peritoneum, in the 

 fat tissue of the gizzard, and on its peritoneal attachment, as 

 well as in the mucous membrane of the air passages. There 

 may also be hyperemia of the spleen and of the kidneys. In 

 less acute cases there is an edematous swelling of the subcu- 

 taneous connective tissue on the neck and breast, also a great 

 amount of a pale yellow, slightly cloudy fluid in the pericardium, 

 which rapidly coagulates in the air. The layers of the pericar- 

 dium sometimes appear to be adherent by fine fibrinous threads. 

 Italian authors mention as a frequent finding a fibrinous exu- 

 date on the pleura and peritoneum (therefore the name of 

 << Typhus exudativus")- 



The comb and the wattles are dark, bluish-red, the con- 

 junctivae show catarrhal swelling. There is a considerable 



