tliMl Ilu'v liiivi- luit ln'i'ii (ilisiMvcd to take liUiod, it is iinilialilc 

 that they feed on t-liylo and tlio partially disintegrated tissues 

 ill their tunnels. 



The Food of Larval Parasitic Nematodes 



The nutrition of the larval parasitic nematodes is funda- 

 mentally like that of adult parasitie or free liviiiK iieiuatodcs 

 subject to the modifications imposed by the environment and 

 the structure of the larvae in question. For example, the re- 

 searches of McCoy (1<)2!)), Lepage (10.S3, in37) and Glaser and 

 StoU (lil.'iiS) on "the free-living stages of Strongylina have re- 

 vealed no essential differences between the mode of nutrition 

 of these immature forms and that of the free-living stages of 

 Rhabdiasidae (see Chu, l!)3(i) and Strongyloididae (see Faust. 

 lO.Si;'). Tlie feeding mechanisms (buccal capsule and rhabdi- 

 toid esophagus) and sources of food (bacteria or fluid organic 

 matter") are essentially the same. The method of feeding of 

 RhabdHix as described by Chitwood and Chitwood (1038, p. 7<i 

 of this series) is probably typical of this group. 



Of the larvae of heteroxenous, parasitic nematodes in their 

 intermediate host, no complete study of the feeding habits is 

 available. But their locations in the intermediate hosts are 

 fundamentally similar to those of various adult forms in pri- 

 mary hosts. Since many of such larvae increase in size without 

 the presence of reserve food stuff, they must secure their niiur- 

 ishment from their lu>st. From the foregoing it would be logi- 

 cal to conclude that larval nematodes in secondary hosts feed as 

 do adult nematodes in analagous positions in primary hosts. 

 Inactive encysted forms are at such low levels of metabolic 

 activit.v in both types of host that simple diffusion is probably 

 more than adequate to maintain the parasite. 



The nutrition of immature nematodes in a primary host is, 

 as far as known, like that of adult nematodes in similar posi 

 tions except for (a) larval nematodes carrying reserve food- 

 stuff and (b) larva! nematodes which may be nourished by dif- 

 fusion. For the rest it is possible to find a larval nematode 

 feeding habit identical with each ma.ior type of adult nematode 

 method of feeding. 



Wetzel (1930) has shown fourth stage Oxyiiris equi to feed 

 like adult Strovgyliis sp. Ortlepp (lfl37) found the same true 

 of larval Gaipcria pachysceHs. According to Ackert (1931), 

 Ascaridia ffalli larvae penetrate the mucosa of the small intes 

 tine and feed much as do Physaloplcra sp. or StronqyJoidrs sn. 



In a study of Cooperia curticei, Andrews (1939) noted the 

 third stage larvae feeding in the lumen of the gut. The fourth 

 stage larvae of this parasite had their anterior ends in the 

 crypts of Liebcrkiihn and grew while in this position indicating 

 the same type of nutrition as that observed in the adult 

 Triehostrongylidae. 



Immature Probstmayria rivipara are found free in the gut 

 tube like ascarids indicating a similar mode of nutrition. Ac- 

 cording to Ransom (1911) immature Oesophapostonm colnm- 

 biaviim feed on the cheesy material in the nodule making their 

 mode of nutrition essentially similar to such forii's as Cnatlm- 

 stoma. Ascarid larvae in the blood stream ingest and digest 

 blood cells, according to Sminiov (193r>), hence resemliling adult 

 Dirofilaria. Wetzel (1931a) has reported a case of what he 

 considers to be extra-intestinal digestion by the fourth stage 

 larva of Dermatoxys veJtgera which attaches to the intestinal 

 mucosa by means of four cephalic hooks, a unique attachment 

 mechanism in nematodes. 



The recent development of culturing techniques for parasitie 

 nematodes promises more information regarding their food. 

 However, to date only one parasitie nematode has been cul- 

 tured throughout its life cycle. This is Neopleciana glaseri 

 which is parasitic in the .Japanese beetle, PopiUia japonic'a 

 (Glaser, 1932). Attempts to grow Haemonchus contortiis of 

 sheep by Lapage (1933) and Glaser and Stoll (1938), and 

 Ascaridia galli of chickens by Ackert, Todd and Tanner (1938) 

 have been only partially successful. Hence, these are included 

 with the discussion of the nutrition of the larval forms. No 

 direct observations of the food of these parasitic nematodes 

 have been made, but the fact that the nematodes have grown 

 and developed in an artificial environment indicates that at 

 least part of the environment is a source of food. Table 1 

 lists these attempts at culturing parasitic nematodes. 



From these considerations it appears that the food of lar- 

 val parasitic nematodes may include bacteria, enteric contents, 

 vascular fluids and elements, and mucosal cells and ti.ssnes. 



Digestion in Parasitic Nematodes 



Most of the parasitic nematodes are placed in intimate 

 contact with the host 's physiological fluids which carry nu- 

 trient materials to its cells. Since these nutrients are in their 

 simplest diffusable form it might be assumed that much of the 

 nourishment of parasitic nematodes is derived from this source 

 and that no true digestion is required. However, a number of 



Tahi,k 1. — Siiiiiiiiary of ulliiiipis Ui ciilliirc iiarasilic nematodes. 



Successful 

 Degree of Culture Normal 



Growth Media host 



Complete Dextrose - veal .lapaneso 

 infusion agar beetle 

 with yeast 

 Complete Fomented po Japanese 

 tato medium hi \: 



Complete Veal infusion & Japanese 

 preservatives beetle 



L a s t Agar, liver ex- Sheep 

 part of tract, sheep 

 fourth blood and kid- 

 larval ney defibrinated 

 stage blood 



Me asur Incubating Chicken 

 able. hens' eggs, 

 growth starch, dextrose, 

 commercial agar 



workers have demonstrated the existence of a true digestion in 

 phylogenetically widely sejiarated parasitic nematodes; hence, 

 it is probable that they all carry on some form of digestion. 

 According to the location of the digestive processes, various 

 workers have distinguished between an intestinal and extra- 

 intestinal digestion. Much of the evidence of extra-intestinal 

 digestion rests upon the occurrence of necrotic or cytolyzed ma- 

 terial around the anterior attached end or within the buccal 

 capsule of parasitic worms. That such .-i i (i"fl>iiiM of the host 

 tissue is so often interpreted as extra-intestinal digestion is 

 somewhat questionable since the effect of parasite excretions, 

 simple trauma, mechanical pressure, and heterophilogenous 

 proteolytic enzymes upon the host tissue would produce many 

 of the conditions described as extra-intestinal digestion. This 

 form of digestion may be possible in some nematodes, how- 

 ever, since Hoeppli (1927) has discovered an epitheliolytic ma- 

 terial present in the anterior end but not in the posterior por- 

 tion of Stroiigyhis. 



The intestinal digestion in nematod"s has been th? sub.ject 

 of work by a considerable number of investigators. Most of 

 the studies have been confined to the demonstrations of en- 

 zymes within extracts of the parasites. Because of the early 

 workers' limited knowledge of enzyme action, much of their 

 results need confirmation before they can be accepted. Flury 

 (1912), for example, made no attempt to crifically evaluate 

 the research of other workers. He simply listed the worker's 

 name and the enzymes which he reported. In little of this 

 early work was the action of bacterial enzymes adequately 

 controlled. The demonstration of a peptolytic enzyme in the 

 gut of Toxocara caiiis by Abderhalden and Heise (1909) is 

 questionable for this reason. Nor was any particular attempt 

 made in the early work to differentiate between intracellular 

 and extracellular enzymes. Most of it was done with extracts 

 of the parasite being studied, and peroxidases and proteases 

 were reported as though the question of their respective origins 

 was of little importance. 



Recent researches have been more accurate. Enigk (1938) 

 showed that Graphidium strigosnm produces an amylase and a 

 protease which are active in the gut tube of the parasite. He 

 was unable to demonstrate a lipase. Chitwood (1938) demon- 

 strated in an extract of the esophagus of Asearis lumiricoides, 

 a proteolytic enzyme which was inactive at its isoelectric point 

 (ph 8.0) and most active in a weak acid solution. The fact 

 that such workers as Wetzel (1928) and Hoeppli and his co- 

 workers have demonstrated digested epithelial cells within the 

 alimentary tracts of certain parasitic nematodes, gives evidence 

 of the existence of ,jroteoIytie enzymes in parasitie nematodes. 

 Enigk 's (1938) finding of a varying reaction in the gut tube 

 of Graphidium strigosiim (pH 7.0 at the ends and 4.4-4.8 in 

 the middle), and Van Someren's (1939) report of an acid re- 

 action in the intestine and rectum of Trichinella spiralis are 

 additional confirmation of the presence of enzymes because al- 

 teration of the reaction of the digestive tract of animals is 

 universally coordinated w^ith the optimum pH for the enzymes 

 present. 



Anticoagulants in blood sucking nematodes have been dem- 

 onstrated by a number of workers. While such products are 

 not primarily digestive, they doubtless prevent blocking of 

 the parasite's alimentary tract with clotted blood; hence, they 

 are an aid to digestion. Such products have been reported by 

 Schwartz (1921) and Hoeppli and Feng (1933). 



Careful consideration of the relative values of the researches 

 demonstrating the presence of enzymes leads to the conclusion 

 that at least one and probably more proteolytic enzymes are 



353 



