886 EXPERIMENT STATION RECORD. [Vol.43 



of secondary lesions regularly in the lungs, rarely in the liver and kidney, and 

 by the later involvement of the liver and kidney (tertiary lesions) through the 

 dissemination of the parasite from the involved lungs. In addition to weak- 

 ness, loss of appetite, and sulphur-colored feces — symptoms which are seen in 

 the spontaneous disease — there is coughing and more or less dyspnea. The 

 inoculated disease has been invariably fatal. 



" The incubation period is commonly 11 days, but varies between 11 and 17 

 days. The appearance of symptoms evidently indicates sufficient involvement 

 of vital organs to interfere seriously with function. The rapid development of 

 the subcutaneous lesion is not attended either by loss of weight or by symp- 

 toms, neither of which appears until after internal organs are involved. 



" In the course of their migration through the tissues from the site of in- 

 oculation, some of the parasites penetrate the veins and are carried to the 

 lungs where they, for the most part, lodge and produce lesions. The disease 

 thus metastasizes by way of the blood stream in a nranner similar to that of 

 certain tumors. The distribution of the parasites is thus governed by their 

 ability to penetrate vessels and by their size and physical properties, which 

 cause them to lodge in capillaries. 



" The expansion and contraction of the lungs evidently serve to dislodge 

 organisms, so that these organs are not as effective filters as the liver. 



" The parasites develop readily in a variety of tissues and organs, mucous 

 membranes, connective tissues, both smooth and striated muscle, lung, liver, 

 and kidney. Macroscopic lesions of the kidney and microscopic lesions of the 

 lung have been found in spontaneous blackhead. 



" The inoculation of chickens has resulted negatively except in newly hatched 

 chicks, in which self-limited local lesions, and in one instance secondary lesions 

 in tlie lungs were produced. 



"A certain proportion of pigeons have proved susceptible to the extent of 

 developing transient self-limited local lesions. Positive results were obtained 

 in 30 per cent of those inoculated. The lesions are es.sentially similar to the. 

 subcutaneous lesions of the turkey, but after developing actively from the fifth 

 to the eighth day undergo regression. Rabbits, guinea pigs, and mice have 

 proved nonsusceptible. 



" Blackhead may be contracted spontaneously from acute cases of its inocu- 

 lated form, probably from the ingestion of food or water contaminated by dis- 

 charges from the respiratory tract. An attempt to transmit the disease 

 through the agency of a species of " blow fly " has failed, but it is possible 

 that this or related species may play a part in the dissemination of the disease. 



Exposure of a young turkey to common fowls, after a long period of isolation, 

 has been followed by the contraction of blackhead, unless the infection is to be 

 attributed to the " blackhead-fed " flies ingested by it 37 days previously. 



" Neither the administration of tartar emetic nor of quinin has served to 

 check the course of the infection. 



" Blackhead may be produced by the introduction of organisms beneath the 

 skin, and is not dependent on the invasion of the tissues by myriads of flagel- 

 lates that have multiplied in the lumen of the gut. No flagellates have appeared 

 in the ceca of newly hatched chickens following the ingestion of large amounts 

 of blackhead virus derived from subcutanoeus and lung lesions. Cases of 

 spontaneous blackhead occur in which there are no demonstrable flagellates in 

 the cecal contents or in the gland lumina. 



" The definite transmission of the disease from one turkey to another by inoc- 

 ulation at once removes the great uncertainty which has attended all experi- 

 ments in the past which have had to depend on the natural and not well under- 

 stood method of transmission by the exposure of healthy turkeys to supposedly 



