CROSS-IXFECTION EXPERIMENTS loi 



Attempts also should be made to infect dogs with the Trichom- 

 onas of rats, pigs, monkeys and cats. 



Giardia 



Giardia has been reported from dogs quite frequently, having 

 first been noted by Grassi (1881). Hegner (1922) states that it 

 possesses a characteristically broad anterior end and proposes the 

 name Giardia canis. Animal-infection experiments seem to have 

 been neglected with the dog, the only results recorded being those 

 of Howitt mentioned by Thomson (1926) in which dogs were 

 reported to have been successfully infected with Giardia from 

 human feces. 



Simon (1922) and Hegner (1922) have proposed a biometric 

 method for differentiating species of Giardia on the basis of their 

 length to breadth ratio. Since, however, the races of Giardia en- 

 countered in man exhibit such a wide variation it seems to the 

 writer (Kessel, 19280^) that many more human cases must be con- 

 sidered as well as more cases of Giardia from the species of 

 animals in question before it will be possible to make any definite 

 statements on this point. The author has seen individual races of 

 Giardia from man that correspond in their measurements and 

 biometric ratios to the Giardice reported from rats, mice, cats, 

 dogs, and monkeys. A single case, or even two or three cases from 

 the cat, the dog, the monkey or any other animal are quite inade- 

 quate as the basis for establishing a new species, since the races of 

 Giardia found in man display such a wide variation in size and 

 shape. 



4. THE DOMESTIC PIG 



The intestinal protozoa of the domestic pig afford an important 

 problem for investigation from the point of view of pubHc health. 

 They are also of interest theoretically because so many of them 

 resemble the protozoa of man. Prowazek (1912) has described an 

 amoeba of the pig which he calls Endamoeha polecki. Smith (1910) 

 described an Endamoeha of the pig which exhibited ability to pene- 

 trate the tissue of the intestine of pigs infected with hog cholera. 

 No cysts of the amoeba were described with certainty. Nieschulz 

 (1924) gives the name E. debliecki to an amoeba which he foimd 

 in pigs. From his account it appears to the writer that he was 

 merely dealing with a small race of the common Endamoeha 

 polecki. Accounts in the literature of the common amoeba of the 



