12 



worm eggs are evidently quite resistant'. It is not known 

 exactly how long they remain alive in soil or water, but they 

 have been kept for several months in moist material without 

 deteriorating. 



This discovery raises several important questions: (1) Is the 

 disease, following the ingestion of worm eggs, true blackhead? 

 (2) Is the worm another host for this parasite, playing a role 

 similar to that of the mosquito for the parasite of malaria in 

 man? (3) Is the blackhead parasite present in all turkeys, 

 lying in wait until some friendly worms come along to give it a 

 start in life? The first of these questions is readily answered. 

 The disease which appears in young turkeys following the 

 ingestion of ripe worm eggs is true blackhead, for the diseased 

 tissues always show the characteristic appearances and great 

 numbers of the specific organism. Whether the worm serves 

 as a host is not yet definitely determined, but it is difficult to 

 see how a germ as large as the parasite of blackhead could 

 be included in the eggs of the worm. The question of the 

 distribution of the blackhead parasite in nature also requires 

 further investigation. The results of the experimental feeding 

 of worm eggs to turkeys indicate that either the blackhead 

 parasite is very prevalent in healthy young turkeys, or that 

 it is associated in some way with the worm in question. 



The part played by worms in the production of blackhead 

 may throw new light on the prevalence of blackhead in young 

 turkeys which are allowed to run with old turkeys and common 

 hens, or on ground that has been frequented by them. We 

 have repeatedly produced blackhead by placing young turkeys, 

 previously isolated, either with a flock of hens or on ground 

 that had been worked over by them. 



The question may be asked w^hether the development of 

 worms in young turkeys is always associated with blackliead. 

 While this disease has always followed the experimental feeding 

 of a quantity of ripe worm eggs, we find in nature worms in 

 greater or smaller numbers in the majority of turkeys. They 

 may even become very numerous without having produced 

 blackhead. Strange to say, we also find some cases of black- 

 head which show very few worms, and others in which no 

 worms are found. It is difficult to explain these discrepancies. 



It is possible that the introduction of a large number of 



