CHAPTER XI 

 CHEMICAL COMPOSITION AND METABOLISM OF NEMATODE PARASITES OF VERTEBRATES, 



AND THE CHEMISTRY OF THEIR ENVIRONMENT 



THEODOR VON BRAND, Department of Biology, Catholic University of America and 

 THEODORE LOUIS JAHN, Department of Zoology, State University of Iowa 



The metabolic procLSses of nematode parasites comprise a 

 subject which has l)een under investigation for many years. 

 Progress in the field, however, has been particularly rapid dur- 

 ing the last decade, and it is the purpose of the present au- 

 thors to present a summary of the known facts of metabolism 

 together with the related subjects of the chemistry of the worms 

 and of their environment. Recent reviews which deal with 

 some of the subject matter here presented are those of Slater 

 (1928), McCoy (1935), Lapage (1S3S) and v. Brand (1934, 

 1938). 



Peculiarities of Environment Which May Influence 

 Metabolism 



The wide differences in the habitats of the various nematode 

 parasites of vertebrates are undoubtedly correlated with wide 

 differences in metabolic processes. The organisms which live in 

 the digestive tract, blood stream, lungs, kidneys, subcutaneous 

 tissue, etc., are subject to quite a variety of environmental 

 conditions. In those cases where open contact with the blood 

 stream or lymph is maintained the parasites are, of course, 

 subjected to an environment very similar to that of the cells of 

 the host body. Whenever a nematode is surrounded by a cyst 

 wall which reduces the availability of oxygen, or is located in 

 a region deprived of free blood circulation, metabolic jirocesses 

 are probably different from the processes in those species which 

 live in the blood stream. Species that live in the digestive tract 

 have an environment which is peculiar in many respects. The 

 chemistry of blood is adequately described elsewhere, and the 

 chemical environment within cysts and in chemically isolated 

 tissues is practically unknown (except for cestode cysts, Schop- 

 fer, 1932). Therefore, the present discussion of environment 

 is limited to the chemistry of the digestive tract. 



From the viewpoint of nematology the chemistry of the in- 

 testinal contents is interesting for several reasons. A thor- 

 ough knowledge of the chemistry of the environment may allow 

 a better understanding of the physiology of the intestinal 

 parasites, it may aid in the formulation of culture media suit- 

 able for growth in vitru (cf. Glaser and Stoll, 1938), and it may 

 shed light on the problems of host specificity and on the possi- 

 bility that experimental modifications of intestinal contents 

 may be of use in controlling the activities of the nematodes. 

 The effect on nematodes of many of the substances found in 

 the intestine has not been studied. In the hope that the pres- 

 ent discussion might serve as a partial outline of substances to 

 be investigated, the authors have included a general discussion 

 of the chemical compounds present. 



THE SEQUENCE OF CHEMICAL EVENTS IN THE 

 DIGESTIVE TRACT 



In any discussion of the chemical composition of the contents 

 of the digestive tract it is necessary to keep in mind the se- 

 quence of events which occurs as the ingesta pass through the 

 alimentary canal. The chemical composition of the contents 

 of the gut varies with diet, with species, and with the state of 

 health. However, in any healthy animal on a constant diet 

 there is a definite sequence to the chemical changes which occur. 



In man, the stomach leccives the mixture of food and saliva. 

 To this is added mucus, pepsin, and hydrochloric acid. The 

 material present in the duodenum is derived from four sources: 

 chyme from the stomach, bile, . pancreatic juice, and succus 

 entericus. The stomach contents when emptied into the duo- 

 denum consist, among other things, of proteoses and peptones, 

 starch, sugars, fat droplets, some fatty acids and glycerol, 

 hydrochloric acid, plant fragments containing cellulose and 

 undigested plant tissue, and water. 



The bile contains mucin, the pigments biliverdin and bili- 

 rubin, the bile salts Na-taurocholate and Na glycocholate, cho- 

 lesterol, lecithin, fats, soaps, inorganic salts and water. The 

 relative amounts of taurocholate and glycocholate vary with 

 the species; the dog, for example, is entirely lacking in glyco- 

 cholate. The pancreatic secretion contains NasCOa and the 

 enzymes trypsin, lipase, and amylopsin. The succus entericus 

 contributes the enzymes erepsin, lipase, maltase, invertase, lac- 

 tase, and rennin, and a large amount of mucus and desqua- 

 mated epithelial cells. Due to partial sterilization of food, or 

 to the action of hydrochloric acid and bile salts, living bac- 

 teria are present only in small numbers in the duodenum and in 



normal men may sometimes be absent (Kellogg, 1933). As 

 tliese materials pass through the duodenum and jejunum diges- 

 tion is completed, and tlie products of digestion and most of 

 the bile salts are absorbed. The bacteria increase in numbers, 

 utilize some of the products of digestion and decompose others. 

 As the material passes through the large intestine water is ab- 

 sorbed, and calcium, magnesium, iron, and phosphates are 

 secreted by the intestinal wall. 



The feces of an animal on a carnivorous diet are composed 

 mostly of the intestinal secretions and bacteria. If vegetables 

 make up a considerable part of the diet, the bulk of the feces 

 is increased, and plant fragments appear in the feces, some- 

 times with the contained plant protoplasm only jiartially di- 

 gested. The large bulk of undigested cellulose stimulates 

 peristalsis, and consequently causes a more rapid passage of 

 ingesta through the intestine, which results in the absorption 

 of less water liy the colon and a more liquid feces. 



The materials which are present in tlie digestive tract and 

 which may affect the metabolism of nemas are for convenience 

 discussed under the following headings: (1) Composition of 

 the intestinal gases, (2) Hydrogen ion concentration, (3) Dis- 

 solved materials (exclusive of gases), (4) Antienzymes. Nema- 

 todes, esi^eeially those which live in tissues, are known to secrete 

 digestive enzymes, but these are more properly discussed under 

 the subject of nutrition of the worms. 



COMPOSITION OF THE INTESTINAL GASES 



The composition of the gases in or in contact with the in- 

 gesta varies greatly in different parts of the digestive tract. 

 The gas tension of the stomach contents varies at different 

 periods following a meal and depends on the amount of air 

 ingested with food. The action of HCl causes a release of 

 bound COj, most of which is probably absorbed either in the 

 stomach or upper intestine. The oxygen ingested with the food 

 apparently undergoes a rapid decrease so that it is almost ab- 

 sent from the intestine below the duodenum. The analyses of 

 von Brand and Weise (1932) show that very little oxygen is 

 introduced into the intestine by the bile. These investigators 

 also studied the oxygen content of fluid intestinal matter and 

 of intestinal gases. They found that the oxygen content of the 

 fluid of both the large and small intestines of almost all ani- 

 mals examined was practically nil. The only exception was 

 one pig which contained quite appreciable amounts of oxygen. 

 This might have been caused by the swallowing of large 

 amounts of air, perhaps at the time of slaughtering. The 

 values for all animals except the pig correspond to about -5 

 percent saturation. The data of several investigators on the 

 oxygen content of intestinal fluids and gases are summarized 

 in Tables 13 and 14. The data in Table 14 demonstrate the ab- 

 sence of oxygen in the gaseous content of the intestine of all 

 animals except the pig. Long and Fenger (1917) found that 

 oxygen was present in appreciable quantities in the in- 

 testinal gases of the pig, and this was confirmed by v. Brand 

 and Weise. It has been assumed by Slater (1925) that the 

 intestinal walls give off oxygen to the intestinal contents during 

 digestion. This has not been proved experimentally, and Long 

 and Fenger (1917) found that the oxygen content was lowest 

 during active digestion. It seems probable (as indicated by 

 the data of Mclver, Redfield, and Benedict, 1926) that oxygen 

 may diffuse inward from the intestinal wall, but it is also very 

 likely that the bacteria present near the wall would consume 

 this immediately so that very little oxygen from this source 

 would ever reach the central portion of the lumen. The avail- 

 able evidence indicates that the environment of intestinal hel- 

 minths is not devoid of oxygen but contains oxygen in only 

 small quantities. Worms which live close to the intestinal wall 

 may have access to larger amounts. In the case of the hook- 

 worm it is apparent from the observations of Wells (1931) that 

 the blood sucking activities represent largely a respiratory 

 function. 



Analyses of intestinal gases other than O: are not numerous. 

 The intestinal gases of man vary with diet. Ruge (1861) gives 

 the following data for percentage composition: 



Diet CO. H= CH. N= 



Vegetables 21-34 1.5-4.0 44-55 10.19 



Meat 813 0.7-3.0 26-37 45-64 



Milk -- 916 43-54 0.9 36-38 



356 



