8 



The Disease-yroducing Germ associated with Blaclxhcad. — The 

 germ or parasite found in this disease is a low form of animal 

 life, consisting of but a single cell and known as a protozoon. 

 This was discovered by Dr. Theobald Smith in 1895, who 

 named it Amwba meleagridis. Our studies have convinced us 

 that it is not a true amoeba but a protozoon of another type 

 making necessary a change in the first or generic name so that 

 it is now called Histomonas meleagridis; but this is unimpor- 

 tant in the present discussion. These parasites are somewhat 

 rounded organisms varying in size but usually slightly larger 

 than blood corpuscles. They occur in great numbers, and the 

 diseased tissues are literally packed with them, like a honey- 

 comb with young bees. That they multiply very rapidly is 

 shown by the myriads produced in the relatively brief period 

 of the disease. Apparently the parasite enters the turkey by 

 way of the gut with the food or water, and under favorable 

 conditions invades the wall of the caecum and proceeds to mul- 

 tiply. Many of the organisms penetrate the veins of the 

 csecum and are then swept in the blood current to the liver. 

 As the vein divides in the liver into numerous small branches 

 or capillaries these organisms lodge here, as they are too large 

 to pass through the smallest capillaries. They then begin to 

 multiply, invade the liver tissue, and produce the spots already 

 mentioned which are so characteristic of the disease. 



We have been careful not to speak of this parasite as the 

 cause of the disease, for although it is always found in the 

 diseased tissue, the conditions which accomplish its introduc- 

 tion into the tissue are just as important from the standpoint 

 of causing the spread of the disease as the parasite itself. 

 Since it is always a portion of the gut that is first attacked, it 

 has been generally assumed that this parasite is taken in with 

 food or water. It might also be assumed that we should be 

 able to produce the disease by feeding these germs to a young 

 turkey, but this is not the case. We may repeatedly stuff 

 young turkeys with large quantities of the diseased tissues con- 

 taining myriads of the parasites without producing any disease. 

 On the contrary, turkeys treated in this manner may grow 

 somewhat faster than others, owing to the rich diet which they 

 receive. Thinking that this germ might in most cases be 

 destroyed by the digestive juice as it traverses the length of 



