Tlic aoi'obio :iiul aiiat'roliii' iiitiogt'ii iiu'talMilism of Axcari.i 

 has been compaiod by v. Brand (l!i34a). The amounts of nitro- 

 gen excreted both in sohible exereta and in eggs were very 

 nearly identical in both cases. He assumed that at least a 

 large part of the X metabolism was involved in the transforma- 

 tion of the protoplasm of the body into that of eggs. He also 

 considered it likely that at least a large i)art of the nitrogen 

 metabolism was always anaerobic. This view is supported by 

 the fact that free-living animals, like tlie leeches, show, in 

 contrast to Ascarix, a marked dift'erence in the amount of nitro- 

 gen e.\creted under aerobic and under anaeroliic conditions. 



DEDUCTIONS CONCERXIXG TIIK MKTABOLISM 



IX riro 



Deductions concerning the nature of the metaliolism of in- 

 ternal parasites can be drawn only from the chemical composi- 

 tion of their surroundings and their metabolism in vitro. Of 

 special interest is the question of whetlier the nematodes para- 

 sitizing the intestine lead an anaerobic or an aerobic life. On 

 the basis of the investigations of Bunge (LSSJ)) and Weinland 

 (1901) the first possibility was accepted for many years as an 

 undisputed fact. More recently certain investigators (Slater, 

 192.'); Mueller, 1928/29; Adam, 1932; Davey, 1938a and b) 

 have held the opposite view, i.e., that tlie worms can get enough 

 oxygen in the intestine to allow an oxidative metabolism. Re- 

 cently V. Brand (193S) has reviewed the question, and he be- 

 lieves that a general answer can not be given. Api)arently the 

 size or relative surface and the presence of respiratory pigments 

 will have a great influence on whether a worm can or can not 

 obtain sufficient oxygen at the low tensions prevailing in the 

 intestine. Large parasites, like Ascaris or Parascaris, must be 

 regarded as predominantly anaerobic organisms. As mentioned 

 above, the.v show a marked fermentative metabolism even in 

 air. Since their oxygen consumption is dependent on the oxygen 

 pressure, one can be reasonably sure that fermentative metabo- 

 lism will be relatively much greater in the intestine. Further 

 signs of their adaptation to an anaerobic life are that the.v 

 are remarkably resistant to the lack of oxygen in vitro and 

 that they are able to excrete the end products of anaerobic 

 metabolism. It seems, however, quite possible that the small 

 amounts of oxygen available in the intestine are not entirely 

 without significance. This may be indicated by the observations 

 that the worms contain some haemoglobin, that stimulated 

 Ascaris die much more rapidly in absence than in presence of 

 oxygen, and finally that they are able to perform under suitable 

 conditions such a clearly aerobic process as the resynthesis of 

 gl.veogen. 



Small nematodes, on the other hand, offer better opportuni- 

 ties for the diffusion of oxygen because of their relatively 

 larger surface. This may explain why the sheep nematodes do 

 not show (Davey, 1937, 1938a and b) the same resistance 

 against lack of oxygen as Ascaris. The conclusion of Davey 

 that these worms lead an aerobic life under natural conditions 

 is, therefore, probably only in apparent contradiction with the 

 statement made above in regard to large helminths. 



An entirel.y different way of getting oxygen may be realized 

 in worms sucking larger amounts of blood from their hosts. 

 According to Wells (1931) the blood sucking activities of hook- 

 worms seem to serve largely as a respiratory function. His data 

 allow the calculation that under optimal conditions 100 gm of 

 worms could obtain 20 gm of oxygen from this source in 24 

 hours. This would be about ten times as much as Harwood and 

 Brown (1934) found to be the actual oxygen consumption. 



No data are known about the metabolism of adult parasitic 

 nematodes which normally live outside the intestine. It is there- 

 fore unnecessary to enter into a similar discussion concerning 

 their metabolism. On the whole one may assume that they will 

 have frequently, though probably not in every case, better op- 

 portunities to get larger amounts of oxygen than the intestinal 

 helminths. 



SYNTHESIS OF RESERVE SUBSTANCES 



There are only a few investigations which concern the ques- 

 tion of the synthesis of reserve substances in parasitic nema- 

 todes. Hoffman (1934) and Kriiger (1936) have shown that 

 the heat production and the o.xygen uptake of ascarids under 

 both anaerobic and aerobic conditions are increased if sugar is 

 present in the surrounding medium. Hirsch and Bretschneider 

 (1937) fed ascarids iron saccharate and concluded from their 

 histological investigation that it was absorbed as colloid and 

 broken down only in a certain part of the intestinal cells into 

 iron and sugar. 



Quantitative determinations of the glycogen content of car- 

 bohydrate-fed ascarids have been performed by Weinland and 

 Ritter (1902). They found no increase in the glycogen con- 

 tent of animals kept in solutions containing various carbohy- 



drates, altliough glucose caused a lowering of the rate of utili- 

 zation of body glycogen. More positive results were achieved 

 by injecting the sugar solutions into the animals. In these ex- 

 periments new glycogen was foJined after injection of glucose 

 and probably levulose. The consumption of body glycogen was 

 decreased by injections of maltose and perhaps galactose, but 

 not by injections of hictose. 



Von Brand and Otto (1938) compared the glycogen content 

 of hookworms from dogs which had been starved for 48 to 72 

 hours before death with those from dogs which had been given 

 so much sugar during a similar 'period that the liver glycogen 

 rose from 0.06 percent to .").04 percent. No difference what- 

 ever in glycogen content of the worms was found. This may be 

 related to the fact that hookworms obtain their food from the 

 tissues rather than from tho lumen of the intestine and there- 

 fore can gain their maximal food requirements even from a 

 starving host. 



So far no experiments have been performed on the deposition 

 of fat in parasitic nematodes except the above mentioned doubt- 

 ful results of Schulte (1917) concerning the fat increase in 

 ascarids under anaerobic conditions. The whole question of 

 synthesis should prove interesting for future investigations. 



Metabolism of Eggs and Larvae 



The eggs of many parasitic nematodes show, like the adults, 

 a surprising degree of resistance to lack of oxygen. The eggs 

 of such forms as Anci/lostoma, Parascaris, Trichoccphalus or 

 yematodiriis can be kept for days or even weeks in the absence 

 of oxygen, but they do not complete their development (Looss, 

 1911;"Bataillon, 19*10; Zawadowski, 1916; Faure-Fremiet, 1913; 

 Zawadowski and Orlow, 1927 ; Zviaginzev, 1934 ; Dinnik and 

 Dinnik, 1937). In Parascaris oxygen is unnecessary only during 

 the early stages, i.e., maturation, fertilization and perhaps the 

 first cleavage stages; for further development oxygen is indis- 

 pensable (Faure-Fremiet, 1913; Szweikowska, 1929; Dyrdow- 

 ska, 1931). The need of oxygen for completion of development 

 seems to be a general requirement, although the stage of de- 

 velopment at which oxygen becomes necessary seems to vary 

 somewhat with different species. Zawadowsky and Schalimow 

 (1S29), Schalimow (1931), and Wendt (1936) conclude that 

 the necessity for oxygen begins in Enterobius vermicularis 

 with the tadpole stage, and in Oxi/iiris eqni with the gastrula 

 stage. Relatively low oxygen pressures, however, are sufficient 

 to insure normal development in Ascaris and Ancylostoma 

 (Brown, 1928; McCoy, 1930). 



The amount of oxygen consumed by one Ascaris egg in de- 

 veloping from the one-cell stage to the motile embryo is about 

 0.002.5 cmm with only slight variations whether the develop- 

 ment is completed in "21 days at 23°C or in 11 days at 30°C 

 (Brown, 1928). Huff (1936) obtained a value of 0.0041 cmm 

 for Ascaris, and Nolf (1932) obtained a value of 0.0027 for the 

 eggs of Trichuris. It is surprising that an Ancylostoma egg re- 

 quires for its development from the morula stage to the fully 

 developed larva almost exactly the same amount of oxygen 

 (0.0028 cmm at 23° C. according to McCoy, 1930) as an As- 

 caris egg, although development of Ancylostoma is completed 

 in about 24 hours. Since these eggs are about the same size, 

 it seems as if the difference in the rate of oxygen consumption 

 mentioned above for the adults of these species is also present 

 in the embryonic stages. 



Huff (1936) observed that the o.xygen consumption of As- 

 caris eggs increased more than five times after removal of the 

 albuminous coating by antiformin. Friedheim (1933) found 

 that the oxygen consumption of Ascaris eggs is considerably 

 increased if they are immersed in a dilute solution of hallo- 

 chrome (a pigment which is a reversible oxidation-reduction 

 system isolated from the polychaete worm Halla parthenopea 

 and which has an aceelcrative eft'eet on respiration). The mech- 

 anism of the increase in respiration by either of these two 

 methods is not known. Friedheim (1933) apparently used mixed 

 stages of fertilized eggs, and there seems to be no reason for 

 assuming that hallochrome could penetrate the egg shell. There- 

 fore, one might expect the acceleration obtained to be due to 

 an increase in the effective oxygen tension or to an increase 

 of respiration in only those eggs on which an impermeable shell 

 had not yet been formed. The experiments of Huff might also 

 be explained as being caused by an increase in effective oxygen 

 tension because of slow diffusion of oxygen through the albumi- 

 nous coat, but no data concerning these possibilities are avail- 

 able. Since the R. Q. is always less than 1.0 (see below) the 

 possible effect of oxygen tension could not be merely to change 

 the ratio of oxidative and fermentative metabolism. The ac- 

 celerations produced by Friedheim (1933) and Huff (1936) 

 must, for the present, be accredited to changes in the rate of 

 oxidative metabolism, and the reasons for the changes re- 

 main obscure. 



36S 



