The question as to whether Ascaris from the pig may be transmitted to man, and its converse, have long been recognised as being of considerable public health importance. Hitherto the evidence, both epidemiological and experimental, is somewhat in favour of the belief that human Ascaris and Ascaris from the pig are not interchangeable as to their respective hosts. Experimental evidence in support of this was supplied in 1922 by Koino, who swallowed a large number of embryonated eggs from the pig form, and although severe pneumonic symptoms were set up by the migrating larvæ, the latter did not complete their development, and no intestinal infestation followed. A similar negative result was obtained by Payne, Ackert and Hartman (1925), from infection experiments performed on themselves and on a rhesus monkey; they also fed large numbers of human Ascaris eggs to pigs but without success. Some epidemiological evidence has also been furnished by these workers, for they indicated that although in Trinidad and Arouca the circumstances were favourable for reciprocal infection, yet the incidence of Ascaris in man and pigs in these regions in no way suggested that such a condition of affairs obtained.