List of Illustrations xi 



FIGintE PAGB 



49. The poultry tick, Argas persicus, adult. (After Laurie) . . 228 



50. The poultry tick larva showing three pairs of legs. (After 



Laurie) 229 



51. The chicken flea, PitJea; graHincB or aOTuni. (After Kaupp) . 231 



52. Head and neck of fowl aHected with generalized favus. (After 



Pearson) 233 



53. The fungus Achoridn schonleinii, which causes favus in poultry 235 



54. Sore-head on comb, eyelids, and skin. (After Hadley and 



Beach) ..... 239 



55. Reproductive organs of a hen. (After Duval) . , . . . 247 



56. Showing a case of incomplete hermaphroditism. (Original) . 252 



57. Oviduct removed from a laying hen and cut open along the point 



of attachment of the ventral ligament. (Original) . . 260 



58. Triple-yolked egg. (Original) 275 



59. Showing shapes of abnormal eggs sometimes found. (From 



von Durski, after Landois) ..... . 279 



60. The normal ovary of a laying hen. (After Kettger, Kirkpat- 



rick, and Jones) 289 



61. Ovary from a hen infected with B. pullorum. (After Rettger, 



Kirkpatrick, and Jones) . 290 



62. Showing how baciUary white diarrhea perpetuates itself in the 



breeding stock. (After Rettger and Stoneburn) . .291 



63. Ten-day-old White Leghorn chicks showing symptoms of bacil- 



lary white diarrhea. (After Rettger and Stoneburn) . . 292 



64. Normal ten-day White Leghorn chicks. (After Rettger and 



Stoneburn) 293 



65. Trachea of a pheasant showing gape worms {Syngamus trache- 



alis). (After M6gnin) 305 



66. A pair of SyngMnua trachealis attached. (After M6gnin) . 305 



67. A ^aii ot Syngamus trachealis. (After M6gnin) . . .307 



68. Sarcoma chicken tumor No. 1. Second generation. (After 



Rous) 316 



69. Chicken tumor XVIII in the gizzard of the original fowl. 



(After Rous and Lange) 317 



70. Osteo-chrondrosarcoma produced by intramuscular injection of 



4 cc. of the Berkfeld filtrate of an extract of chicken tumor 

 No. "VII. (After Rous and Murphy) 318 



71. The growth shown in figure 70 after it had been sawed open. 



(After Rous and Murphy) 319 



72. Cysto-adenoma on the serosa of the intestine. (After Pickens) 322 



