4 BULLETIN 817^ U. S. DEPT. OF AGKICULTUEE. 



PROBABLE IDENTITY OF ASCARIS LUMBRICOIDES AND ASCARIS 



SUUM. 



The common intestinal roundworm of man {Ascaris lumhricoides) 

 and the corresponding parasite of the pig {A. suwm Goeze or ^4. 

 suilla Dujardin) are morphologically indistinguishable and prob- 

 ably are specifically identical. Whether or not infection of man from 

 worms harbored by the pig, and vice versa, commonly occurs is un- 

 known and it has not yet been shown by experiment whether or not 

 the offspring from worms harbored by one host can reach fertile 

 maturity in the other. Although there is no good reason for con- 

 sidering the two forms to be distinct, in the present paper the pig 

 Ascaris will be referred to as A. sumrh and the human Ascaris as 

 A. lumbricoides, so that it may be clear in any given case whether 

 the parasite came from a pig or from a human host. 



EGG STAGE OF ASCARIS. 



INCUBATION. 



^^lien deposited by the adult female in the intestine of the host 

 animal the Qgg of Ascaris is in an early stage of segmentation. 

 Segmentation progresses during the passage of the Qgg through the 

 intestine. If the Qgg is not promptly eliminated in the feces of the 

 host, however, segmentation does not continue and development of the 

 embryo comes to a standstill. Martin (1913) found by experiments 

 in vitro that at the body temperature of the host segmentation pro- 

 gresses rapidly up to a certain limit, but development of the embryo 

 is completed only at lower temperatures. Because of the inhibiting 

 effect of the body temperature it is necessary for the eggs to pass 

 out of the intestine of the host before they can develop to the infec- 

 tive stage. Outside the body the development of the eggs is chiefly 

 influenced by three factors — temperature, moisture, and oxygen 

 supply. At low temperatures development proceeds slowly and 

 may stop entirely if the temperature is low enough, so that the time 

 required for the embryo to develop to the final stage reached in the 

 egg may vary from a few days to many months and possibly several 

 years. 



Martin (1913) found the optimum temperature for the develop- 

 ment of the eggs of Ascaris vituloruon (of the ox) and A. suum to be 

 about 33° C. We have noted that a considerable proportion of the 

 eggs of A. suxira- kept at this temperature contain fully developed 

 embryos at the end of 10 days, and practically all complete their de- 

 velopment within a month. In the absence of moisture, development 

 is inhibited and extreme dryness may ultimately destroy the vitality 

 of the eggs. The moisture requirements, however, are slight. Ross 

 (1916) found that eggs of A. lumhricoides placed on glass slides and 



