432 ANNUAL REPORT SI^IITHSONIAN INSTITUTION, 19 39 



cerning trichinae in about 8,000,000 hogs from which samples were 

 examined up to 1906. In addition, information is given on recent 

 findings on the incidence of trichinae in hogs, as follows : 



Out of 6,622 samples of pork obtained from grain-fed hogs origi- 

 nating in various hog-growing centers of the United States, only 

 60 (0.91 percent) were found to be infected with trichinae. Out of 

 6,484 samples of pork obtained from hogs fed on garbage as collected, 

 286 (4.41 percent) were found to be infected, while out of 1,987 

 samples of pork obtained from hogs that had been fed on cooked 

 garbage, only 11 (0.55 percent) were infected; the samples from 

 the garbage-fed hogs, like those from the grain-fed hogs, were ex- 

 amined by the digestion method. Additional data involving the 

 examination of a total of 13,162 diaphragms from as many grain-fed 

 hogs and 10,500 diaphragms from as many hogs fed on garbage as 

 collected show an incidence of trichinae in the latter six times 

 that in the former. 



The logical inference from these data is that the feeding of un- 

 cooked garbage favors the spread of trichina infection among hogs, 

 and that cooking of garbage is an effective method of sharply reduc- 

 ing the incidence of trichinae in this class of hogs. 



An analysis of the data, with reference to the samples of pork 

 that contained trichinae, shows that the degree of infection with 

 these parasites was rather light, and that if the samples in question 

 had been examined microscopically, a large proportion of the posi- 

 tives, discovered by the digestion technique, would have been 

 overlooked. 



Data obtained as a result of experimental infection of pigs with 

 varying doses of trichina larvae, show that the host animals in ques- 

 tion showed no readily recognizable symptoms when the resulting 

 infection was characterized by the presence of less than 800 to 900 

 larvae per gram of diaphragm muscle tissue. Pigs with heavier 

 infections did show clinical symptoms during the active stage of the 

 disease, including digestive disturbances, muscular stiffness, inap- 

 petence, fever, edema, and other conditions, all the symptoms not 

 being shown by each animal experimentally infected with relatively 

 large doses of larvae, and the symptoms as a whole not being diag- 

 nostic of any particular swine disease. 



The evidence presented in this paper shows that swine may suc- 

 cumb to heavy infections with trichinae, death occurring as early as 

 7 to 10 days after infection. 



Considering the minimum number of trichinae per gram of dia- 

 phragm muscle tissue associated with clinical symptoms during the 

 active stage of the disease, only 1 out of the 357 trichina-infested hogs 

 that came to light as a result of digesting samples from 15,333 hogs. 



