CHAPTER VI 



ASCARIS LUMBRICOIDES AS A TYPE OF THE 

 NEMATODA 



TECHNICAL SUGGESTIONS 



Specimens of the pig ascaris are to be obtained from slaughter 

 houses and preserved for dissection in 10 per cent formalin. The 

 larger horse ascaris makes an excellent object for laboratory dissection 

 but is rather difficult to obtain. 



Eggs should be removed from the terminal portions of the uteri of 

 fresh specimens and cultured at summer temperature under a shallow 

 layer of 2 per cent formalin to prevent contamination. All stages 

 will be found for study in about two weeks. 



Experimental animals — mice, rats, or guinea-pigs — may be fed 

 cultures of infective eggs on bread and the pathologic conditions in 

 the lungs demonstrated a week later. 



The migrating larvae can most easily be recovered by chopping the 

 liver and lungs and placing them in the simplified Baermann apparatus 

 (p. 107). Then they will migrate out into the warm water and settle 

 to the bottom. 



For demonstrating the larva? in the liver tissue, a heavily infected 

 animal should be killed about the fourth day after the experimental 

 feeding and small portions of the liver fixed in Zenker's fluid. For 

 stages in the lung, it is better to fix in acetic-alcohol (glacial acetic, 

 1 part; absolute alcohol, 3 parts) some 10 days after infection. Para- 

 affin sections of 10 to 15 n in thickness should be cut, stained in Dela- 

 field's haematoxylin, and mounted in the usual manner. 



For the infection experiments the dog ascaris, Toxocara canis, or 

 Toxocara mystax from the cat will serve as well. Demonstrations of 

 these common parasites should be shown and their eggs studied in 

 comparison with those of Ascaris lumbricoides. 



At this time there should also be demonstrated specimens of 

 Gordiacea and of Acanthocejthala, forms which can hardly be given 

 special attention in an introductory course. 



CHARACTERISTICS OF THE ASCAROIDEA 



The class Nematoda contains species of great economic impor- 

 tance to animals and plants. Many of the species parasitic in 

 animals pass part of their cycle free in the soil. The majority 

 of the species of the group are oviparous, although some are 

 viviparous. The larvae undergo typically two molts before they 

 are in the infective stage. As an introductory type Ascaris 



33 



