11 



Transmission of Blackhead. 



The opinion is sometimes expressed by turkey raisers that 

 "the disease is not contagious," implying that it is not readily 

 transmitted from sick to healthy turkeys. There is consider- 

 able evidence to support this view. Experimental attempts 

 to produce blackliead by exposing healthy young turkeys to 

 those suffering from blackhead rarely give positive results. 

 The irregularity of the results of such experimental exposures 

 suggests that the transmission of the disease depends on some 

 other condition or conditions than on the mere transference 

 of the parasite of blackliead to healthy birds. It has already 

 been pointed out that young turkeys may be fed great quan- 

 tities of this germ without producing the disease. This failure 

 to contract the disease, however, is not due to any lack of 

 susceptibility, for it is known that all turkeys, apparently with- 

 out exception, develop the disease when the parasites are 

 inoculated directly into the tissues. 



An attempt has been made to lower the natural resistance 

 by cold and wetting. A turkey chick was chilled by sitting in 

 cool water a few minutes daily for several days, and at the 

 same time was fed large amounts of diseased tissue containing 

 living blackliead germs. The only difference shown in the 

 subsequent development of this turkey was that he became 

 the largest and smartest one of the lot in which he w^as hatched. 



Intestinal IJ^orms as a Factor in Transviission. — ■ Experiments 

 carried out quite recently by Graybill and Smith have resulted 

 in a very interesting discovery. They found that by feeding 

 young turkeys the eggs of a small worm which is commonly 

 found in the cseca of both common fowls and turkeys, they 

 always produce blackhead. This worm, called Heterakis yap- 

 illosa, about one-half an inch in length, is very widespread, 

 and is probably to be found in almost all flocks of fowls, and 

 especialh' in yards where fowls have been kept for some time. 

 The microscopic eggs of these worms are discharged in the 

 droppings of fowls, but have to develop on the ground for 

 from two to three weeks with a favorable amount of warmth 

 and moisture before they are ready to hatch. When such 

 "ripe" eggs are eaten by other fowls or turkeys they hatch out 

 and the young worms grow to maturity in the caeca. These 



