4 CONTROL SERIES No. 58 



eggs are incubated and hatched, infected chicks may be the result. The in- 

 fected clucks may die or survive and transmit the infection to other chicks. 

 Chicks which survive an acute attack of the disease may grow to maturity, 

 may remain infected, and thus become "carriers" or transmitters of the dis- 

 ease. The disease might become almost self-limited if the organism were not 

 transmissible from the adult to the chick by means of the egg. 



Photograph 1. — Ovaries Removed from Hens. 

 Specimens numhered 1 and 3 infected with pnllorum disease; No. 2, a normal ovary. 



Losses Resulting from the Disease 



Chick mortality. — The greatest loss encountered from this disease is among 

 the chicks. A slight to a heavj^ mortality is often observed among infected 

 cliicks, depending upon certain factors mentioned earlier in the discussion. 



Reduced fertility and hatchabilify. — The disease may be responsible for re- 

 duced fertility and hatchability to such an extent that it may inflict a great 

 loss upon poultrymen. Numerous investigators have substantiated this ob- 

 servation. 



Under-developed birds. — Among chicks that have passed through an attack 

 of the disease, one generally finds a great variation in size and rate of 

 growth. This has also been observed among artificially infected chicks which 

 were given equal doses of infective material. Apparently chicks do not all 

 possess the same degree of resistance and may not be re-infected to the same 

 extent by contaminated litter and droppings. Such observations were made 

 at this laboratory when a suspension of the causative organism was admin- 

 istered, by mouth, witii a pipette, to 52 strong vigorous chicks, 72 hours old, 

 which had been procured from a pullorum disease-free flock. The infective 

 dose was rather Iieavy, .since 44 ])er cent of the chicks died during the first 

 six weeks following initial exj)osure. At this time tlie weights of the 29 re- 

 maining cliicks varied from 90 to 558 grams, as shown in the following table: 



