PARASITES 367 



Longistriata musculi dikivlvnts, 1935. — The trichostrongylc, L. musculi, 

 parasitic in the intestine of the mouse, was lirst described by Dikmans (9) 

 in 1935, and in the same year its life history was reported by Schwartz and 

 AHcata (34). It is a small worm, the adult males measuring 3.25 to 4.5 mm. 

 long and the adult females 4.25 to 6.75 mm. The anterior end of the body is 

 usually coiled in a loose spiral. 



In life-history studies Schwartz and Alicata found that the eggs soon after 

 being eliminated from the host hatched into larvae which after but one molt 

 reached the infective stage. Thus, there occurred a deviation from the 

 usual four molts characteristic of the development of nematodes generally. 

 Both infection through the mouth and through the skin resulted in the 

 appearance of worms in the small intestine which developed with two molts 

 into adults. The usual migration through the lungs was not essential for 

 development. In some cases the skin-penetrating larvae did pass through 

 the lungs, but these were considered exceptional. 



Nippostrongylus muris (yokogawa, 1920). — Yokogawa (44) first 

 described this parasite from wild Norway rats caught near Baltimore. Of 

 26 rats taken, 24 were infected. It has also been found in the house mouse 

 caught in the same locality. Although Porter (28) found in a comparative 

 study of N . muris in rats and mice that mice were quite susceptible to infec- 

 tion, he concluded that the mouse is a somewhat abnormal host, as demon- 

 strated by the longer prepatent period, smaller percentage development, 

 lower egg production, and shorter duration of infestation in mice than in 

 rats. The parasite has been used extensively for studies of resistance in 

 which the rat has been employed. 



The worms appear red, filiform, and somewhat narrowed anteriorly. 

 The adult males are 3 to 4 mm. in length with a maximum thickness of 0.085 

 to 0.1 mm., and the females are 4 to 6 mm. long with a maximum thickness 

 of 0.09 to 0.12 mm. They are usually found in clumps or nests in the 

 anterior half of the intestine. These nests appear red due to the excess blood 

 in the villi of the region. Yokogawa (45) found that the infective larvae 

 could enter the host both via the mouth or through the skin, the latter being 

 most eft'ective. They go to the lungs where they undergo a part of their 

 development, and later complete their development to maturity in the intes- 

 tine. The eggs are ellipsoidal with very thin shells. They average 

 58 /x X 33 IX. 



N . muris is decidedly pathogenic if present in large numbers. Africa (i) 

 described heavily infected animals as having been manifestly ill as shown by 

 their emaciated condition. Their eves were dull and their hair ruffled. 



