1«6 MASS. EXPEIUMENT STATION BILLE^ITN 278 



The intravenous injections of filtered tracheal exudates into susceptible birds 

 indicate that the living virus can circulate in the blood in sufficient quantities to 

 cause general infections, but immune bodies are developed in this tissue, so that 

 it has been impossible to demonstrate its presence by direct methods. 



The nervous system is apparently rarely affected, although the hen shown in 

 Figure 2 contracted the disease naturally and developed chon>a from which it 

 never fully recovered. The hen was kei)t under observation for six months. 

 At necropsy a hemorrhage was found on the ventral surface of the cerebellum. 

 A small blood vessel had ruptured in the cerebellar tissues and blood had flowed 

 into the space between the meninges and the cerebelhun, forming a clot. This 

 rupture and blood clot appeared like those occasionally found in the respiratory, 

 circulatory, and visceral organs of fowls dying of I'cute infectious laryngotrachei- 

 tis. A slight infiltration in the brain tissues around the clot indicated that the 

 blood was being slowly absorbed. In another set of experiments two hickens 

 were successfully inoculated with infectious laryngotracheitis from the brain of 

 a pullet dying of the disease. Blood clots were not found in this pullet, although 

 the brain material was preserved by Swift's (1921) method and other chickens 

 were inoculated later, confirming the infectiousness of the tissues examined. 



Birds showing visible symptoms of infectious laryngotracheitis are called 

 acute cases. (Figure 3.) An attempt has been made to determine the length of 

 time acute cases eliminate virus, because of the importance of such knowledge 

 in developing control measures. Since the experiments reported in this bulletin 

 were started in November, 1930, individual tests have been made on 504 birds, 

 with ten viruses from widely separated places in Massachusetts, four from 

 California, and four from New Jersey. The number of cases of acute infectious 

 laryngotracheitis among the birds studied, and the number of flays during which 

 thev eliminated virus were as follows: 



Totals and average 17 487 0.27 



Chronic Carriers 



Birds which show no visible symptoms of the disease and yet eliminate virus 

 are called chrcjnic carriers. The chronic carrier stage was not found at all ages, 

 for 160 chickens, inoculated when two weeks old and younger, were included in 

 these studies and when tested kiter no chronic; carriers were found among them. 

 Chronic carriers were found among the i)ullets. cockerels and nldcr birds, as 

 follows: 



\'irus ('lii'oiiir ("ari'iers 

 Ma.ssachusetts .strains 9 



California strains 3 



New .Jersey strains 2 



Total 14 



