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A note on the reduction in the iron content of meat in relation to iron deficiency
A NOTE ON THE REDUCTION IN THE IRON CONTENT O F M E A T IN R E L A T I O N T O I R O N D E F I C I E N C Y
S. A. JENKINS Pye Research Centre, Walnut Tree Manor. Haughle)" Green. Suffolk. IPI4 3RS. Great Britain
(Received: 8 January, 1977)
S UM,I,IA R Y
The blood haemoglobin concentration, serum iron levels and muscle iron content o f cattle, pigs, lambs and chickens were determined at the time of slaughter. There was a marked reduction in the iron content o f pork, beef and chicken when compared with the figures quoted b.v McCance & Widdowson (1960). The possible relationship between a reduction in the iron content o f meat and the aetiology o f iron deficieno' is discussed.
INTRODUCTION
There is substantial evidence that the prevalence of iron deficiency is high in highly industrialised countries (Garby et al., 1969; Elwood, 1968; Kilpatrick, 1961; US Committee on Iron Deficiency, 1968; Blix, 1968). The majority of the population with depleted iron stores has no abnormal blood loss (Cook & Finch, 1975), suggesting that some other factor, probably nutritional, is important in the aetiology of iron deficiency. The amount ofhaem iron present in the diet could be this aetiological factor, since it is much more readily absorbed than non-haem iron (Callender et al., 1957; Chodos et al., 1957; Moore & Dubach, 1951 and 1956; Layrisse & Martinez-Torres, 1972). Moreover, the presence of meat in a meal enhances the absorption of nonhaem iron (Cook & Finch, 1975). The present study indicates a marked reduction in the iron content of meat eaten in Britain which might be contributory to the. prevalence of iron deficiency. 277 Meat Science (1) ( 1977)--'~ Applied Science Publishers Ltd. England, 1977
Printed in Great Britain
278
s A. JENKINS MATERIALS AND METHODS
Animals Blood and meat samples were obtained from cattle, pigs, lambs and chickens at the time of slaughter. The cattle consisted of a mixture of steers and heifers reared specifically for meat, and older cows being slaughtered because they were barren or had stopped lactating. The meat from the steers was intended for consumption in this country, while that of the cows was for export to France. The chickens and pigs were all reared on intensive farming systems, whereas the lambs were grass reared. Details of the age of all the animals except the cows were obtained from the suppliers. The age of the cows was estimated by examination of the teeth.
Sampling techniques Blood samples from the cattle, lambs and pigs were obtained from the jugular vein. The chickens were sampled by heart puncture. Samples of the internal massetter of the cattle, diaphragm of pigs and lambs, and the pectoral muscle of the chickens were obtained after the animals had been exsanguinated. The muscle samples were cleared of visible fat and connective tissue, weighed and frozen to await analysis.
ANALYTICAL PROCEDURES
Blood haemoglobin levels were determined by the method of van Kampen & Zijlstra (1961). The conversion of haemoglobin to haemoglobincyanide derivatives was performed immediately after collection, and the concentration subsequently determined in the laboratory. Blood for the determination of serum iron was chilled after collection and the serum separated from the whole blood in the laboratory. Samples showing any signs of haemolysis were discarded. The serum iron concentration was determined according to the method of Lauber (1965). Muscle samples were wet ashed in a mixture of concentrated sulphuric acid and 50 ~o hydrogen peroxide using the method recommended by the Analytical Methods Committee (1967). The iron content of the muscle was determined on an atomic absorption spectrophotometer (EEL 240) according to the manufacturer's recommended procedure.
RESULTS
The haemoglobin concentration, serum iron levels, and muscle iron content of the cattle, sheep, pigs and chickens are shown in Table I. No clinical signs of iron deficiency as measured by the blood haemoglobin concentration were observed in
M E A T I R O N C O N T E N T IN R E L A T I O N T O I R O N D E F I C I E N C Y
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~o
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._- .~-~
~~ +1~+1+1+1+1
v z
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z
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+1 +1 +1 +1 +1 +1 .~.o ..1 Z O
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~
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,
~ z O
.
<~ 7..7 7_~ t: _ i
7"
=.-_:
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279
280
s.A. JESKINS
the pigs, sheep, cattle or chickens. Similarly, the serum iron levels were within the normal range for all four types of animal studied. Further, there was no significant (P > 0-05) age-related difference between the haemoglobin concentrations or serum iron levels of the cattle. Considerable variation occurred in the iron content of the muscles from the four types of animal studied, the highest concentration being found in the internal massetter of the cattle and the lowest in the pectoral muscle of the chickens. Further, there was a variation in the iron content of the internal massetter muscle of the cattle, the muscle from the cows containing significantly more (P < 0-01) iron than that from the younger steers or heifers.
DISCUSSION
The iron content ofthe internal massetter muscle of the cowswas significantly higher than that of the younger steers or heifers. Since no significant differences were observed between either the serum iron levels or haemoglobin concentration of the cows, heifers and steers, the difference in the iron content of the muscle cannot be attributed to variations in either of these parameters. Further, it seems unlikely that the difference in the iron content of the muscle of cows and beef cattle is sex-linked, since the internal massetter iron content of the cows was significantly higher than that of the heifers. The myoglobin concentration of mammalian muscle increases with age (Lawrie, 1950). The steers and heifers sampled in this study were considerably younger than the cows and consequently differencesin the muscle iron content between the two groups of animals may be due to an age-related variation in their myoglobin content. According to McCance & Widdowson (1960), the iron content of raw beef, raw pork and raw chicken is 3.7, 1.4 and 0-7 mg Fe/100g of meat respectively. These values are substantially greater than those reported here and suggest that the iron content of chicken, pork and beef has decreased since the last analyses were performed. This suggestion is supported in the case of beef and pork by the recently published values of 1-7 and 0.8 mg Fe/100 g edible portion for each of these meats respectively (Manual of Nutrition, ! 976). The latter authority cites a value of 1.5 mg Fe/100g of meat for chicken which is considerably higher than either the value presented here or that given by McCance & Widdowson (1960). However, this discrepancy may be due to the type of muscle analysed since the value of 1.5 mg Fe/100 g of meat (Manual of Nutrition, 1976) refers to the whole bird, whereas the levels presented here, and those given by McCance & Widdowson (1960) refer to the pectoral muscle only. It is difficult to account for the apparent reduction in the iron content of beef, pork and chicken muscle. During the last two decades there have been substantial changes in farm practice, with more and more livestock being reared on intensive farming systems. One of the consequences of changes in the methods of animal husbandry is
MEAT IRON C O N T E N T IN RELATION T O IRON DEFICIENCY
281
that animals are now slaughtered at a younger age. Thus, the reduced iron content of meat observed in the present study may be partly or wholly due to a reduced muscle myoglobin content, since the latter has been shown to increase with age (Lawrie, 1950). Alternatively, it is possible that the reduced iron content of the meat is due to an increased fat content, since meat from intensively reared animals has a higher fat content than meat from animals free to range and select their own food (Crawford, 1968; Crawford et al., 1971). Further work is necessary to establish which ofeither of these hypotheses is correct. McCance & Widdowson (1960) quote no figures for the iron content of lamb, presumably because this meat did not form any a p p r ~ i a b l e part of the British diet when their tables were drawn up. However, these authors quote an iron content of 1-7 mg Fe/100 g for raw lean mutton, which is considerably higher than the 1.09 mg Fe/100 g we obtained for lamb diaphragm or the 1.3 mg Fe/100 g cited in the M a n u a l o f Nutrition (1976). Since the farming of sheep has changed very little over the last two or three decades, it seems unlikely that differences between the iron content of mutton (McCance & Widdowson, 1960), and those reported here for lamb, can be accounted for by changes in farming practice. However, as with cattle, the difference in the iron content o f m u t t o n and lamb may be due to an age-related variation in the muscle myoglobin content. Hence, the change in dietary habits in this country from consumption of mutton to consumption of lamb, may have had the overall effect of reducing the iron intake from this particular type of meat. Meat has two important roles in iron metabolism. Firstly, it is a very good source of biologically available iron (Callender et al., 1957: Chodos.et al., 1957; Moore & Dubach, 1951 and 1956; Layrisse & Martinez-Torres, 1972), and secondly, it enhances the absorption of less available forms of iron (Cook & Finch, 1975). Therefore, a reduction in the iron content of meat of such magnitude as suggested by this study, may have profound effects on the aetiology of iron deficiency, since less biologically available haem iron is present in the diet, and this in turn will reduce the absorption of non-haem iron. Since ascorbic acid enhances the absorption of nonhaem iron (Bj6rn-Rasmussen, 1973 and 1974; Layrisse & Martinez-Torres, 1972; Sayers et al., 1967 and 1973), the situation may be worsened in Britain as reports suggest that a large percentage of the population have reduced Vitamin C intakes during winter (Allen et al., 1969; Lonergan et al., 1975). Consequently, a reduction in the iron content of meat, coupled with a reduced intake of Vitamin C, may be responsible for the prevalence of iron deficiency in an apparently well fed population such as our own.
ACKNOWLEDGEMENTS
The author wishes to acknowledge the technical assistance of Mr J. A. Rawlings, and the co-operation of the British Beef Company, St Edmunds Bacon Factory, John Rannoch Ltd and E. Pilgrim and Sons.
282
s A. JENKINS
REFERENCES ALLEN. R. J. L., BROCK, M. & BROADBENT,S. R. (1969). Br. J. Nutr., 22, 555. Analytical Methods Committee (1967). Analyst, 92, 403. BJ(3RN-RASMUSSEN, E. (1973). Scand. J. Haemat., ! !, 391. BJORN-RASMUSSEN. E. (1974). Nutr. Metab.. 16, 94. Bux, G. (ed.) (1968). Occurrence, causes and prevention o]" nutritional anaemias, Symp. Swed. N utr. Found. 6, Alnqvist and Wiksell, Stockholm. CALLENDER, S. T.~ MALLE'I'I',B. J. & SMITH, l~I. D. (1957). Br. J. Haemat.. 3, 186. CHODOS. R. B., ROSS,J. F., APT., L., POLLYCUE.M. & HALKET,J, A. E. (1957). J. Clin. Invest.. 36, 314. COOK, J. D. & FINCH. C. A. (1975). West. J. Med., 122, 474. CI~,WFORD, M. A. (1968). Lancet, 1, 1329. CRAWFORD. M. A., GALE, M. M., WOODFORD, M. H. & CASPED,N. M. (1971). Int. J. Bioehem., 1,295. ELWOOO, P. C. (1968). Proc. Nutr. Soc., 27, 14, GARBY, L., IRNELL, L. &- WERNER, 1. (1969). Acta ,tied. Scand., 185, 107. Iron Deficiency in the United States, Committee on Iron Deficiency (I 968). J. Am. Med. Assoc., 203,407. KAMPEN, E. J. VAN& ZIJLSTRA, W. G. (1961). Clin. Chim, Acta, 6, 538. KILPATRICK. G. S. (1961). Br. Med. J., 2, 1736. LAL'BER. K. (1965). Z. Klin. Chem.. 3, 96. LAWRtE, R. A. (1950). J. Agric. Sci., 40, 356. LAYRISSE, M. & MARTINEZ-TORRES,C. (1972). Am. J. Clin. Nutr., 25, 401. LONERGAN, M. E., MtLNE, J. S., MAULE, M. M. & WlLLIAMSON,J. (1975). Brit. J. Nutr., 34, 517. Manual o f Nutrition (1976). Ministry of Agriculture, Fisheries and Food, London. HMSO. MC'CANCE,R. A. & WIDDOWSON, E. M. (1960). The composition of foods. Medical Research Coancil Special Report Series No. 297. MOORE. C. V. & DUBACH, R. V. (1951). Trans. Ass. Am. Phy~ns., 64, 245. MOORE, C. V. & DUBACH, R. V. (1956). J. Am. Med. Assoc., 162, 245. SAYERS, M. H., LYNCH. S. R., CHARLTON, R. W. & BOTHWELL,T. H. (1967). Brit. J. Nutr., 31,367. SAYERS. M. H., LYNCIt, S. R., JACOBS, P., CHARLTON, R. W., BOTHWELL,T. H., WALKER, R. B. & MAYET, F. (1973). Brit. J. ttaemat., 24, 209.
S. A. JENKINS Pye Research Centre, Walnut Tree Manor. Haughle)" Green. Suffolk. IPI4 3RS. Great Britain
(Received: 8 January, 1977)
S UM,I,IA R Y
The blood haemoglobin concentration, serum iron levels and muscle iron content o f cattle, pigs, lambs and chickens were determined at the time of slaughter. There was a marked reduction in the iron content o f pork, beef and chicken when compared with the figures quoted b.v McCance & Widdowson (1960). The possible relationship between a reduction in the iron content o f meat and the aetiology o f iron deficieno' is discussed.
INTRODUCTION
There is substantial evidence that the prevalence of iron deficiency is high in highly industrialised countries (Garby et al., 1969; Elwood, 1968; Kilpatrick, 1961; US Committee on Iron Deficiency, 1968; Blix, 1968). The majority of the population with depleted iron stores has no abnormal blood loss (Cook & Finch, 1975), suggesting that some other factor, probably nutritional, is important in the aetiology of iron deficiency. The amount ofhaem iron present in the diet could be this aetiological factor, since it is much more readily absorbed than non-haem iron (Callender et al., 1957; Chodos et al., 1957; Moore & Dubach, 1951 and 1956; Layrisse & Martinez-Torres, 1972). Moreover, the presence of meat in a meal enhances the absorption of nonhaem iron (Cook & Finch, 1975). The present study indicates a marked reduction in the iron content of meat eaten in Britain which might be contributory to the. prevalence of iron deficiency. 277 Meat Science (1) ( 1977)--'~ Applied Science Publishers Ltd. England, 1977
Printed in Great Britain
278
s A. JENKINS MATERIALS AND METHODS
Animals Blood and meat samples were obtained from cattle, pigs, lambs and chickens at the time of slaughter. The cattle consisted of a mixture of steers and heifers reared specifically for meat, and older cows being slaughtered because they were barren or had stopped lactating. The meat from the steers was intended for consumption in this country, while that of the cows was for export to France. The chickens and pigs were all reared on intensive farming systems, whereas the lambs were grass reared. Details of the age of all the animals except the cows were obtained from the suppliers. The age of the cows was estimated by examination of the teeth.
Sampling techniques Blood samples from the cattle, lambs and pigs were obtained from the jugular vein. The chickens were sampled by heart puncture. Samples of the internal massetter of the cattle, diaphragm of pigs and lambs, and the pectoral muscle of the chickens were obtained after the animals had been exsanguinated. The muscle samples were cleared of visible fat and connective tissue, weighed and frozen to await analysis.
ANALYTICAL PROCEDURES
Blood haemoglobin levels were determined by the method of van Kampen & Zijlstra (1961). The conversion of haemoglobin to haemoglobincyanide derivatives was performed immediately after collection, and the concentration subsequently determined in the laboratory. Blood for the determination of serum iron was chilled after collection and the serum separated from the whole blood in the laboratory. Samples showing any signs of haemolysis were discarded. The serum iron concentration was determined according to the method of Lauber (1965). Muscle samples were wet ashed in a mixture of concentrated sulphuric acid and 50 ~o hydrogen peroxide using the method recommended by the Analytical Methods Committee (1967). The iron content of the muscle was determined on an atomic absorption spectrophotometer (EEL 240) according to the manufacturer's recommended procedure.
RESULTS
The haemoglobin concentration, serum iron levels, and muscle iron content of the cattle, sheep, pigs and chickens are shown in Table I. No clinical signs of iron deficiency as measured by the blood haemoglobin concentration were observed in
M E A T I R O N C O N T E N T IN R E L A T I O N T O I R O N D E F I C I E N C Y
,.+. p-
G
. . . .
~o
+1+1+1+t+1~
<
u_ rZ
._- .~-~
~~ +1~+1+1+1+1
v z
f, ,..1
P+
z
.5
<
+1 +1 +1 +1 +1 +1 .~.o ..1 Z O
N 2~
N
z <
~
z
,
~ z O
.
<~ 7..7 7_~ t: _ i
7"
=.-_:
q
~ ,.~ N
i..,
279
280
s.A. JESKINS
the pigs, sheep, cattle or chickens. Similarly, the serum iron levels were within the normal range for all four types of animal studied. Further, there was no significant (P > 0-05) age-related difference between the haemoglobin concentrations or serum iron levels of the cattle. Considerable variation occurred in the iron content of the muscles from the four types of animal studied, the highest concentration being found in the internal massetter of the cattle and the lowest in the pectoral muscle of the chickens. Further, there was a variation in the iron content of the internal massetter muscle of the cattle, the muscle from the cows containing significantly more (P < 0-01) iron than that from the younger steers or heifers.
DISCUSSION
The iron content ofthe internal massetter muscle of the cowswas significantly higher than that of the younger steers or heifers. Since no significant differences were observed between either the serum iron levels or haemoglobin concentration of the cows, heifers and steers, the difference in the iron content of the muscle cannot be attributed to variations in either of these parameters. Further, it seems unlikely that the difference in the iron content of the muscle of cows and beef cattle is sex-linked, since the internal massetter iron content of the cows was significantly higher than that of the heifers. The myoglobin concentration of mammalian muscle increases with age (Lawrie, 1950). The steers and heifers sampled in this study were considerably younger than the cows and consequently differencesin the muscle iron content between the two groups of animals may be due to an age-related variation in their myoglobin content. According to McCance & Widdowson (1960), the iron content of raw beef, raw pork and raw chicken is 3.7, 1.4 and 0-7 mg Fe/100g of meat respectively. These values are substantially greater than those reported here and suggest that the iron content of chicken, pork and beef has decreased since the last analyses were performed. This suggestion is supported in the case of beef and pork by the recently published values of 1-7 and 0.8 mg Fe/100 g edible portion for each of these meats respectively (Manual of Nutrition, ! 976). The latter authority cites a value of 1.5 mg Fe/100g of meat for chicken which is considerably higher than either the value presented here or that given by McCance & Widdowson (1960). However, this discrepancy may be due to the type of muscle analysed since the value of 1.5 mg Fe/100 g of meat (Manual of Nutrition, 1976) refers to the whole bird, whereas the levels presented here, and those given by McCance & Widdowson (1960) refer to the pectoral muscle only. It is difficult to account for the apparent reduction in the iron content of beef, pork and chicken muscle. During the last two decades there have been substantial changes in farm practice, with more and more livestock being reared on intensive farming systems. One of the consequences of changes in the methods of animal husbandry is
MEAT IRON C O N T E N T IN RELATION T O IRON DEFICIENCY
281
that animals are now slaughtered at a younger age. Thus, the reduced iron content of meat observed in the present study may be partly or wholly due to a reduced muscle myoglobin content, since the latter has been shown to increase with age (Lawrie, 1950). Alternatively, it is possible that the reduced iron content of the meat is due to an increased fat content, since meat from intensively reared animals has a higher fat content than meat from animals free to range and select their own food (Crawford, 1968; Crawford et al., 1971). Further work is necessary to establish which ofeither of these hypotheses is correct. McCance & Widdowson (1960) quote no figures for the iron content of lamb, presumably because this meat did not form any a p p r ~ i a b l e part of the British diet when their tables were drawn up. However, these authors quote an iron content of 1-7 mg Fe/100 g for raw lean mutton, which is considerably higher than the 1.09 mg Fe/100 g we obtained for lamb diaphragm or the 1.3 mg Fe/100 g cited in the M a n u a l o f Nutrition (1976). Since the farming of sheep has changed very little over the last two or three decades, it seems unlikely that differences between the iron content of mutton (McCance & Widdowson, 1960), and those reported here for lamb, can be accounted for by changes in farming practice. However, as with cattle, the difference in the iron content o f m u t t o n and lamb may be due to an age-related variation in the muscle myoglobin content. Hence, the change in dietary habits in this country from consumption of mutton to consumption of lamb, may have had the overall effect of reducing the iron intake from this particular type of meat. Meat has two important roles in iron metabolism. Firstly, it is a very good source of biologically available iron (Callender et al., 1957: Chodos.et al., 1957; Moore & Dubach, 1951 and 1956; Layrisse & Martinez-Torres, 1972), and secondly, it enhances the absorption of less available forms of iron (Cook & Finch, 1975). Therefore, a reduction in the iron content of meat of such magnitude as suggested by this study, may have profound effects on the aetiology of iron deficiency, since less biologically available haem iron is present in the diet, and this in turn will reduce the absorption of non-haem iron. Since ascorbic acid enhances the absorption of nonhaem iron (Bj6rn-Rasmussen, 1973 and 1974; Layrisse & Martinez-Torres, 1972; Sayers et al., 1967 and 1973), the situation may be worsened in Britain as reports suggest that a large percentage of the population have reduced Vitamin C intakes during winter (Allen et al., 1969; Lonergan et al., 1975). Consequently, a reduction in the iron content of meat, coupled with a reduced intake of Vitamin C, may be responsible for the prevalence of iron deficiency in an apparently well fed population such as our own.
ACKNOWLEDGEMENTS
The author wishes to acknowledge the technical assistance of Mr J. A. Rawlings, and the co-operation of the British Beef Company, St Edmunds Bacon Factory, John Rannoch Ltd and E. Pilgrim and Sons.
282
s A. JENKINS
REFERENCES ALLEN. R. J. L., BROCK, M. & BROADBENT,S. R. (1969). Br. J. Nutr., 22, 555. Analytical Methods Committee (1967). Analyst, 92, 403. BJ(3RN-RASMUSSEN, E. (1973). Scand. J. Haemat., ! !, 391. BJORN-RASMUSSEN. E. (1974). Nutr. Metab.. 16, 94. Bux, G. (ed.) (1968). Occurrence, causes and prevention o]" nutritional anaemias, Symp. Swed. N utr. Found. 6, Alnqvist and Wiksell, Stockholm. CALLENDER, S. T.~ MALLE'I'I',B. J. & SMITH, l~I. D. (1957). Br. J. Haemat.. 3, 186. CHODOS. R. B., ROSS,J. F., APT., L., POLLYCUE.M. & HALKET,J, A. E. (1957). J. Clin. Invest.. 36, 314. COOK, J. D. & FINCH. C. A. (1975). West. J. Med., 122, 474. CI~,WFORD, M. A. (1968). Lancet, 1, 1329. CRAWFORD. M. A., GALE, M. M., WOODFORD, M. H. & CASPED,N. M. (1971). Int. J. Bioehem., 1,295. ELWOOO, P. C. (1968). Proc. Nutr. Soc., 27, 14, GARBY, L., IRNELL, L. &- WERNER, 1. (1969). Acta ,tied. Scand., 185, 107. Iron Deficiency in the United States, Committee on Iron Deficiency (I 968). J. Am. Med. Assoc., 203,407. KAMPEN, E. J. VAN& ZIJLSTRA, W. G. (1961). Clin. Chim, Acta, 6, 538. KILPATRICK. G. S. (1961). Br. Med. J., 2, 1736. LAL'BER. K. (1965). Z. Klin. Chem.. 3, 96. LAWRtE, R. A. (1950). J. Agric. Sci., 40, 356. LAYRISSE, M. & MARTINEZ-TORRES,C. (1972). Am. J. Clin. Nutr., 25, 401. LONERGAN, M. E., MtLNE, J. S., MAULE, M. M. & WlLLIAMSON,J. (1975). Brit. J. Nutr., 34, 517. Manual o f Nutrition (1976). Ministry of Agriculture, Fisheries and Food, London. HMSO. MC'CANCE,R. A. & WIDDOWSON, E. M. (1960). The composition of foods. Medical Research Coancil Special Report Series No. 297. MOORE. C. V. & DUBACH, R. V. (1951). Trans. Ass. Am. Phy~ns., 64, 245. MOORE, C. V. & DUBACH, R. V. (1956). J. Am. Med. Assoc., 162, 245. SAYERS, M. H., LYNCH. S. R., CHARLTON, R. W. & BOTHWELL,T. H. (1967). Brit. J. Nutr., 31,367. SAYERS. M. H., LYNCIt, S. R., JACOBS, P., CHARLTON, R. W., BOTHWELL,T. H., WALKER, R. B. & MAYET, F. (1973). Brit. J. ttaemat., 24, 209.