16 CONTROL SERIES No. 63 



In addition to the fact that the disease may be transmitted to the progeny 

 by means of the egg, it is known that incubated infective eggs are capable of 

 producing the disease when fed to poultry or to other animals. Jones (dS) re- 

 ported a septicemic outbreak of pullorum disease among adult hens caused by 

 the feeding of incubated eggs that contained 5. pullorum. Rettger (78) stated 

 that eggs harboring large numbers of the organism produce abnormal conditions 

 when fed to young chicks, adult fowls, young rabbits, guinea pigs, and kittens. 

 Mathews (63) observed field cases where infection was introduced through the 

 feeding of incubated, infertile eggs. He also was able to infect eight pullets by 

 feeding incubated naturally infective eggs. Olney (68) reported a severe outbreak 

 of the disease among adult rabbits as a result of feeding incubated, infertile eggs. 



While S. pullorum has been isolated from fresh eggs, the possibility of such 

 eggs being infective when eaten by animals has not been definitely established. 

 Van Heelsbergen (91) reports that very often thin-shelled eggs are laid by car- 

 riers affected with salpingitis. These carriers do not always lay their eggs in the 

 trap nests, thereby affording other birds an opportunity to pick the shell and eat 

 the infective contents. According to investigations, such eggs are very infec- 

 tious for adult hens. Other investigatiors (48, 84, 92) report that fresh eggs laid 

 by infected birds may reproduce the disease when eaten by other birds. 



It is known that frequently eggs are laid on the floor and dropping boards. 

 Especially is this true for pullets when they first reach sexual maturity. If the 

 eggs are broken, an opportunity for birds to eat or come into contact with the 

 contents is afforded. Some birds even develop a habit of egg-picking and egg- 

 eating. While field and laboratory observations suggest that pullorum disease 

 may be disseminated in such a manner, experimental evidence has been lacking. 

 Therefore, an investigation was designed to determine whether non-infected 

 females may contract pullorum disease through eating fresh eggs laid by infected 

 hens. 



Procedure 



Eighteen birds, free from pullorum disease, were divided into two groups. 



In Group A, the birds (5 hens and 7 pullets) were held in individual cages. 

 Their diet consisted of cracked grain, laying mash, and one egg from infected 

 hens a day. Prior to the feeding of the eggs, an effort was made to determine 

 which reacting birds were laying infective eggs. One hundred eggs, laid by 9 

 birds, were examined bacteriologically for S. pullorum. The organism was isolated 

 from eggs laid by all of these birds with the exception of 2. S. pullorum was re- 

 covered from 12 per cent of the total eggs cultured. Recognizing the fact that 

 the elimination of the organism through the egg is neither constant nor per- 

 manent, it was considered advisable to determine the approximate incidence of 

 the organism in the eggs which were to be fed. The initial method of feeding the 

 egg was to break it and place it upon the litter. Since not all birds ate the egg 

 given in this manner, the method of feeding was changed. A broken egg was 

 placed in each feed cup daily. This method also proved unsatisfactory and was 

 further modified. An egg was mixed with sufficient dry mash in the feed cup to 

 make a semi-dry mixture, which was readily eaten by all birds. Cracked grain 

 was added to the diet whenever the egg-mash mixture had been eaten. All 

 birds were fed a minimum of 31 feedings and one received as many as 65. Each 

 bird was tested by the macroscopic tube agglutination method in dilutions of 

 1:10 and higher at weekly intervals. 



The antigen used was a composite of three known agglutinable strains of 

 5. pullorum. The organisms were grown on nutrient agar for 72 hours at a tem- 

 perature of 37 ° C. The growth was then washed off with phenolated, physiologi- 

 cal saline solution and the suspension standardized to a turbidity corresponding 



