476 EXPEKIMENT STATION RECORD. lYol. 43 



another experiment, three incubator turkeys received embryonated eggs plus 

 turkey feces from an infectious flock. All contracted blackhead. Three re- 

 ceived embryonated eggs alone; all contracted blackhead. Three received 

 turkey feces only ; none contracted blackhead. Three controls received nothing; 

 one showed blackhead lesions at the autopsy. 



" In a final experiment three turkeys were fed cultures of feces from the 

 ceca of diseased turkeys, three were fed cultures of feces of old turkeys from 

 an infected flock, and three controls were fed nothing. None contracted black- 

 head. The cultures of feces were prepared precisely as were the earlier ones 

 containing Heterakis eggs, but without the latter. From these experiments, 

 it becomes evident that blackhead may be produced in healthy incubator-raised 

 turkeys, reared in the open in an environment where blackhead occurs, but out 

 of direct contact with old turkeys and other poultry, by feeding cultures of 

 embryonated eggs of H. papulosa, prepared by cutting up the worms in isotonic 

 salt solution and incubating the suspension at room temperature. 



" The production of acute blackhead by feeding embryonated eggs to turkeys 

 in whose ceca adults of H. papulosa are already present seems incompre- 

 hensible at first thought. A tentative explanation to be offered is that the 

 worms when invading the ceca in large numbers break down the resistance of 

 the bird, which is able to protect itself against a few. This may account 

 for the very irregular occurrence of cases in contact with older recovered birds 

 on infected grounds. The role of Heterakis as a preliminary agent may also 

 account for the continuing high mortality in turkeys in which the disease has 

 been operating for so many generations to eliminate the most susceptible. It 

 now seems highly probable that the turkey has become relatively resistant to 

 the invasion of the protozoan parasite acting alone, and that such invasion 

 may require other agencies. Whether H. papulosa is the only, or at any rate 

 the chief accessory agent or whether there are others, living or inert, which 

 when ingested by the turkey assist in preparing the way for the destructive 

 invasion of the walls of the ceca and the liver by Amoeba meleagridis is a 

 question now open to solution by experimentation. The relation of common 

 poultry to outbreaks of blackhead may be accounted for, at least in part, by the 

 fact that they are hosts of H. papulosa. How frequently they also carry A. 

 meleagridis remains to be determined." 



The flagellate character and reclassification of the parasite producing 

 "blackhead" in turkeys. — Histomonas (n. g. ) meleagridis (Smith), 

 E. E. Tyzzer {Jour. ParasitoL, 6 {1920), No. 3, pp. 124-131, pi. i).— The early 

 studies of the author led to the suggestion of the flagellate character of this 

 parasite (E. S. R., 41, p. 685). Subsequent observations are here recorded, 

 showing that this organism may under certain conditions exhibit characteristic 

 flagellate motility. The proof that it is not an amoeba makes necessary its 

 reclassification, for which the generic name Histomonas is proposed and is 

 characterized as follows : 



" Histomonas n. g., plemorphic, parasitic Tetramitidse with amoeba-like 

 phases of development within tissues of host. The kinetic structures associated 

 with blepharoplat, intraprotoplasmic during amoeba-like phase. Nuclear division 

 trichomonad in type with well-developed paradesmose." 



RTJEAL ENGINEERING. 



Irrigation, M. F. de Magalhaes {Escola Agr. " Luis de Queiros," Piracicaha, 

 Brazil, Bol. 5 {1920), pp. 38, figs. 25). — Irrigation practice in some of the south- 

 ern States in both arid and humid regions is reviewed, and analogies drawn 

 with conditions in Brazil. 



