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The trapped plasma correction factor in the blood of pigs
J. COMP.
PATH.
THE
1970.
VOL.
163
80.
TRAPPED
PLASMA IN
THE
CORRECTION
BLOOD
OF
FACTOR
PIGS
BY D. M. ANDERSON J.R.C.
Institute
of Animal
Physiology,
Babraham,
Cambridge
INTRODUCTION
it was realised as early as 1915 that centrifugation of samples of blood did not expel all the plasma from the red cell column (Keith. Rowntree and Geraghty, 1915). Since then the amount of plasma remaining in the red cell column has been studied in samples of blood from man, dog, horse, goat, ox, rabbit, sheep and rat (Owen and Powers, 1953). The reported extent of the trapped plasma has varied enormously both within and between species, much of the variation presumably being due to differences in techniques, both of measuring haematocrit and of determining trapped plasma. The most reliable estimates of the volume of trapped plasma which have been made in samples of human blood suggest that the haematocrit is between 095 and 0.97 of the determined volume (Gregersen and Rawson, 1959; Owen and Powers, 1953). Hlad and Holmes (1953), after studies on human blood, suggested that a constant correction factor could not exist because the degree of packing of the red cells in the haematocrit tube varied with the haematocrit. Hodgetts (1959), using sheep blood, suggested that the trapped plasma could be estimated more accurately if the haematocrit was taken into account and that within the haematocrit range 20 per cent. to 60 per cent. the amount of trapped plasma was given by the equation -Trapped plasma = 2.26 +0*03x, where x = haematocrit and the determination wad made at 4,756 x g for 60 minutes. Talbot and Swenson (1963) reported that in saruples of pig blood the trapped plasma ranged from 1 to 6 per cent., with a mean of 3 per cent. The haematocrit was determined using the “micro” haematocrit method. No information on whether any relation existed between the extent of the trapped plasma and the haematocrit was given, nor were any estimates given of the extent of trapped plasma when haematocrit was determined using lower centrifugal forces. ‘The work now reported was undertaken to investigate these points and also to determine whether there was any effect of age on the amount of trapped plasma.
During the first few weeks of life pig blood undergoes a number of changes (Dunne, 1964) ; for example, the proportion of reticulocytes alters, and it seemed possible that a trapped plasma correction derived from blood of adult pigs might not br applicable to the blood of younger animals.
METHODS
blood of pigs aged from 3 to 365 days was collected from the anterior vcna cava. and heparinized immediately. Six micro-haematocrit determinations were made on
164
TRAPPED
PLASMA
CORRECTION
FAC’I’OR
1X
PORCIKE
BLOOD
each sample, the blood being subjected to a force of 11,000 x g for 10 minutes and thr, haematocrit read on a reader with a 10 inch scale. Haematocrit readings were alscj obtained from each sample using standard Wintrohe tubes. In this case a forcrb of 3,000 x g was applied and readings were made after 15, 30 and 60 niinutes. Trapped plasma was determined using radio-iodinated human serunl albumin (R.I.H.S.A. from The Radio Chemical Centre, Amersham, Bucks.) as a marker. The R.I.H.S.A. supplied (1 mCi in 1.5 ml. at delivery) was diluted between 50 peg cent. and 100 per cent. with 0.9 per cent. saline solution according to the amount of decay of I”“. Using a precipitation method, the R.I.H.S.A. was found to contain less than 1 per cent. free I131. Approximately 0.2 to 0.3 ml. of this diluted solution was added to 10 rd. blood. Both Wintrobe and micro-haematocrit determinations were then made on the blood sample. The radio-activity of three 0.5 ml. plasma samples and three 0.5 ml. samples of whole blood was assessed by counting each sample for two periods of 40 seconds. The total number of counts recorded in this period varied from 25,000 to 40,000. The counting was done in a Panax D.657 using a NaI Lvell type crystal with E.H.T. set at 1,500 volts and the discriminator voltage at 20 volts. A background count was made with either no sample or a sample of untreated plasma from the same animal in place. There was no difference between the background counts with or without a sample in place. The counter had a paralysis time of 50 micro seconds and the observed counts were corrected for this. The percentage plasma in each blood sample was estimated from the comparison of the counts per second of O-5 ml. plasma and of 0.5 ml. whole blood. Since the 1131 was contained exclusively in the plasma, per cent. plasma in sample =- Nth XT NtP and
Ntp = true
per cent. where
counts/O*5
ml. plasma
IOO-(- Ntb Ntp and the trapped
plasma
correction
Ntb
= true counts/O.5
therefore X-
factor
the true
ml. blood
haematocrit
=
per cent.
Ht (F) = where Ho
Ht
=
true
haematocrit
and Ho = observed haematocrit. Normally no alteration of the haematocrit of each blood sample was made, but in a few instances a large sample of blood was obtained and from this a number of 10 ml. samples of blood with haematocrits ranging from 20 per cent. to 60 per cent. were made up.
RESULTS
The mean trapped plasma correction factor (F) for pigs blood of all ages and haematocrits was 0.955 + S.D. 0.015. The amount of trapped plasma could not be reduced even after 30 minutes at 11,000 x g. When “F” was plottted against the
haematocrit of the blood sample there was no discernable relation between trapped plasma and haematocrit (Fig. 1). Each result in this figure was obtained from blood from a different animal. In the experiments in which a number of blood samples of widely different haematocrits were made up from one large blood sample there was again no relation between trapped plasma and haematocrit. There was no relation between the amount of trapped plasma in the blood and the age of the pig from which it was drawn (Fig. 2).
165
D. M. ANDERSON Fig.
1.
PS9
l l
r
t
1Q.g7.*c-------2 -0
-----
go*
l
.g
0.95
k cJ
F
l l
3 al i
l
l
2
--------
1SD,_ _
-----------_ l
0
l
MEAN
l _
3-e)
-*-
-
-
-
-
-
l
l
_
-
_
-
-
_
_
LS.0.
_
_
l 0.93
l
-
t 0.91
i 25
30
HaemZxrit
35
45
55
50
(%) The relation
between
“F”
and haematocrit.
The mean
and the S.D. are shown.
Fig. 2.
0.99
l
f
l
LG.97----
--------
3
-
3-
- - - -
l
l
-
-
-
_
-
-‘shoe-
_
l
l l
2 LL
MEAN l
,s
-
0’95
-
&ALL
AGES
l
l
l 8
-e _-------_-
E
&-------a-
-------
‘s.DLl
k
u
0.93
-
0.91
i I
I
I
30
10
50
Age in days ‘The relation
between
“F”
and the age of the pig.
The mean
of all ages and the S.D. areshown.
70
166
TRAPPED
PLASMA
CORRECTION
FACTOR
IN
PORCINE
BLOOD
There was little difference in the haematocrit of the same blood sample measured by Wintrobe and ‘Lmicro” methods. In Table 1 a comparison of lilt. results obtained by the two methods is shown. The mean “micro” haematocrit M as 32.87 + S.E. 1.19 and the mean Wintrobe haematocrit (3,000 s for 30 minutes) was 33.26 rt S.E. 1.14. This difference was not significant. The age of the pig did not affect the agreement between the haematocrits derived by the t\vo methods.
TABLE THE
Microhaernntocrit
24.1 25.3 27.7 35.8
33.4 37.4 33.4 38.9
33.7
1
HAEMATOCRIT (%) OF SAMPLES OF PIG BLOOD AS DETERMINED MICROHAEMATOCRIT METHOD OR WNTROBE TUBES
Wintrobe
Microhaemotocnt
24.3 25.3 29.5 36.1 34.4 37-5 34.0 39.2 34.3
BY THE
IVintrobe
31.2
33.0
34,a
34.8 28.4
27.7 25.1
34.4 33.6 35.0
2.54 34.4 33.7 35.0
38.1
38.2
41.1
41.2
In the determination of Wintrobe haematocrits the time during which the samples were centrifuged appeared to have little effect. In the set of samples mentioned in the previous paragraph the mean Wintrobe haematocrit after 15 minutes at 3,000 x g was 34.0 per cent., after 30 minutes 33.26 per cent. and after 60 minutes 33.13 per cent. The difference between the 15 and 30 minute estimates just failed to reach significance (0.05 < P < O*l), while there was no significant difference between the values obtained after 30 and 60 minutes treatment. DISCUSSION
The most striking point about the results obtained in the present experiments in the lack of correlation between the amount of trapped plasma and the haematocrit. Such a correlation has been demonstrated in the blood of the sheep and of man (Chaplin and Mollison, 1952) and is considered to result from the decrease in the mean relative centrifugal force (RCF) applied to the red cell column as the length of the column increases towards the axis of the centrifuge. This result has most often been demonstrated using a large number of samples of blood of varying haematocrit which have been made up from less than five large blood samples. In this way all variables which affect trapped plasma except hacrnatocrit have been kept to a minimum. When this was done in pig blood no correlation between trapped plasma and haematocrit could be demonstrated. In fact in such experiments the amount of trapped plasma was extremely constant; when the haematocrit of one sample was altered to 28.2 per cent., 37.3 per cent. and 48.2 per cent., the values of ‘F’ were O-963, 0.955 and 0.958 respectively. The most likely explanation is that the combinations of RCF and time used in the present experiments to determine Wintrobe haematocrit were such that the
D.
M.
ANDERSON
167
decreases in RCF brought about by different lengths of red cell column were not important. Obviously this must be the case using the ‘micro’ technique with the blood of all species, since the length of the red cell column is not constant in replicates of the same blood sample, yet the method is very repeatable. The reason for the ease with which minimum values of trapped plasma were obtained using Wintrobe tubes may be related to the marked tendency towards rouleaux formation and high sedimentation rates exhibited by pig erythrocytes (Schalm, 1961). Thus, compared with sheep blood which does not readily form rouleaux, the centrifugal force applied to the red cells in pig blood will be greater at a constant angular velocity and radius because of the greater mass of the rouleaux as compared with individual red cells. The tendency to form rouleaux will not however have any effect on the final degreee of packing achieved (Ponder, 1952). The possibility was also considered that, since RCF is a function of both the radius and the speed of rotation of the centrifuge, then in the centrifuge used in the present experiments, the alteration in mean RCF brought about by changes in the mean length of the red cell column in the Wintrobe tubes was less then in other designs of centrifuge. It is possible, however, to calculate that in the centrifuge used in the present experiments which achieved 2,950 x g at 3,800 rpm., the mean RCF in the red cell column dropped from 2,747 i: g at a haematocrit of 26 per cent. to 2,585 x g at haematocrit 46 per cent., a drop of 5.9 per cent. In the centrifuge used by Hodgetts (1959) which achieved 3,044 x g at 4,000 rpm. a similar change in haematocrit lowered mean RCF from 2,811 x g to 2,632 x g> a drop of 6.4 per cent. ‘The drop in mean RCF was, therefore, of the same order in both cases but it is apparent that correcting equations as suggested by Hodgetts f 1959), apph. only to haematocrit derived in a centrifuge of the same radius. It appears, therefore, that minimum \.alues of trapped plasma are readily achieved in samples of pig blood, even at relatively low centrifugal forces. Ho\ve\ cr, once the amount of trapped plasma has been reduced to the levels shown in Fig. 1 no amount of additional treatment will reduce the amount. This is in direct contrast to the results obtained with human blood by Jackson and Nutt (195 I) who reported that centrifugation in excess of 4,000 x g for 15 minutes reduced trapped plasma almost to zero. Leeson and Reeve (195 1) suggested on theoretical grounds that to obtain less than 9 per cent. trapped plasma some deformation of the erythrocytcs must take place. The present results however agree with the statement by Ponder (1952) that when red cells are ‘more than about 95 per cent. packed, relativrly tremendous forces are required to pack them further.’
SUMMARY
The trapped plasma correction factor in centrifuged samples of pig blood was 0.955 f 0.015 (S.D.) M’ mrmum * values of trapped plasma were quickly achieved using both high and low centrifugal forces. There was no relation between the amount of trapped plasma and the haematocrit of the sample. The age of the pig from which the blood sample was obtained did not affect the amount of trapped plasn la.
168
TRAPPED
PLASMA
CORRECTION
FACTOR
IN
PORCINB
RI.OOD
REFERENCES
Chaplin, H., and Mollison, P. L. (1952). Blood, 1, 1227. Dunne, H. W. (1964). Diseases of Swine. 2nd Ed. Iowa State University Press; :\mes, Iowa. Gregersen, M. I., and Rawson, R. (1959). Physiol. Revs. 39, 307. Hlad, C. J., and Holmes, J. H. (1953). J. up@. Physiol, 5, 457. Hodgetts, V. Elizabeth (1959). Ausr. J. exp. Biol Med. Sci., 37, 97. Jackson, M. D., and Nutt, M. E. (1951). J. Physiol. Lond., 115, 197. Keith, H. M., Rowantree, L. G., and Geraghty, J. T. (1915). Arch. int. Med., 16, 517. Leeson, D., and Reeve, E. B. (1951). J. Physiol. Lond., 115, 129. Owen, C. A., and Powers, M. H. (1953). J. appl. Physiol., 5, 323. Ponder, E. (1952). Haemolysis and Related Phenomena, J. and A. Churchill; London. Schalm, 0. W. (1961). Veterinary Haematology, Bailliere, Tindall and Cox; London. Talbot, R. B., and Swenson, M. J. (1963). Amer. J. vet. Res., 24, 467. [Received
for publication,
june
12th, 19691
PATH.
THE
1970.
VOL.
163
80.
TRAPPED
PLASMA IN
THE
CORRECTION
BLOOD
OF
FACTOR
PIGS
BY D. M. ANDERSON J.R.C.
Institute
of Animal
Physiology,
Babraham,
Cambridge
INTRODUCTION
it was realised as early as 1915 that centrifugation of samples of blood did not expel all the plasma from the red cell column (Keith. Rowntree and Geraghty, 1915). Since then the amount of plasma remaining in the red cell column has been studied in samples of blood from man, dog, horse, goat, ox, rabbit, sheep and rat (Owen and Powers, 1953). The reported extent of the trapped plasma has varied enormously both within and between species, much of the variation presumably being due to differences in techniques, both of measuring haematocrit and of determining trapped plasma. The most reliable estimates of the volume of trapped plasma which have been made in samples of human blood suggest that the haematocrit is between 095 and 0.97 of the determined volume (Gregersen and Rawson, 1959; Owen and Powers, 1953). Hlad and Holmes (1953), after studies on human blood, suggested that a constant correction factor could not exist because the degree of packing of the red cells in the haematocrit tube varied with the haematocrit. Hodgetts (1959), using sheep blood, suggested that the trapped plasma could be estimated more accurately if the haematocrit was taken into account and that within the haematocrit range 20 per cent. to 60 per cent. the amount of trapped plasma was given by the equation -Trapped plasma = 2.26 +0*03x, where x = haematocrit and the determination wad made at 4,756 x g for 60 minutes. Talbot and Swenson (1963) reported that in saruples of pig blood the trapped plasma ranged from 1 to 6 per cent., with a mean of 3 per cent. The haematocrit was determined using the “micro” haematocrit method. No information on whether any relation existed between the extent of the trapped plasma and the haematocrit was given, nor were any estimates given of the extent of trapped plasma when haematocrit was determined using lower centrifugal forces. ‘The work now reported was undertaken to investigate these points and also to determine whether there was any effect of age on the amount of trapped plasma.
During the first few weeks of life pig blood undergoes a number of changes (Dunne, 1964) ; for example, the proportion of reticulocytes alters, and it seemed possible that a trapped plasma correction derived from blood of adult pigs might not br applicable to the blood of younger animals.
METHODS
blood of pigs aged from 3 to 365 days was collected from the anterior vcna cava. and heparinized immediately. Six micro-haematocrit determinations were made on
164
TRAPPED
PLASMA
CORRECTION
FAC’I’OR
1X
PORCIKE
BLOOD
each sample, the blood being subjected to a force of 11,000 x g for 10 minutes and thr, haematocrit read on a reader with a 10 inch scale. Haematocrit readings were alscj obtained from each sample using standard Wintrohe tubes. In this case a forcrb of 3,000 x g was applied and readings were made after 15, 30 and 60 niinutes. Trapped plasma was determined using radio-iodinated human serunl albumin (R.I.H.S.A. from The Radio Chemical Centre, Amersham, Bucks.) as a marker. The R.I.H.S.A. supplied (1 mCi in 1.5 ml. at delivery) was diluted between 50 peg cent. and 100 per cent. with 0.9 per cent. saline solution according to the amount of decay of I”“. Using a precipitation method, the R.I.H.S.A. was found to contain less than 1 per cent. free I131. Approximately 0.2 to 0.3 ml. of this diluted solution was added to 10 rd. blood. Both Wintrobe and micro-haematocrit determinations were then made on the blood sample. The radio-activity of three 0.5 ml. plasma samples and three 0.5 ml. samples of whole blood was assessed by counting each sample for two periods of 40 seconds. The total number of counts recorded in this period varied from 25,000 to 40,000. The counting was done in a Panax D.657 using a NaI Lvell type crystal with E.H.T. set at 1,500 volts and the discriminator voltage at 20 volts. A background count was made with either no sample or a sample of untreated plasma from the same animal in place. There was no difference between the background counts with or without a sample in place. The counter had a paralysis time of 50 micro seconds and the observed counts were corrected for this. The percentage plasma in each blood sample was estimated from the comparison of the counts per second of O-5 ml. plasma and of 0.5 ml. whole blood. Since the 1131 was contained exclusively in the plasma, per cent. plasma in sample =- Nth XT NtP and
Ntp = true
per cent. where
counts/O*5
ml. plasma
IOO-(- Ntb Ntp and the trapped
plasma
correction
Ntb
= true counts/O.5
therefore X-
factor
the true
ml. blood
haematocrit
=
per cent.
Ht (F) = where Ho
Ht
=
true
haematocrit
and Ho = observed haematocrit. Normally no alteration of the haematocrit of each blood sample was made, but in a few instances a large sample of blood was obtained and from this a number of 10 ml. samples of blood with haematocrits ranging from 20 per cent. to 60 per cent. were made up.
RESULTS
The mean trapped plasma correction factor (F) for pigs blood of all ages and haematocrits was 0.955 + S.D. 0.015. The amount of trapped plasma could not be reduced even after 30 minutes at 11,000 x g. When “F” was plottted against the
haematocrit of the blood sample there was no discernable relation between trapped plasma and haematocrit (Fig. 1). Each result in this figure was obtained from blood from a different animal. In the experiments in which a number of blood samples of widely different haematocrits were made up from one large blood sample there was again no relation between trapped plasma and haematocrit. There was no relation between the amount of trapped plasma in the blood and the age of the pig from which it was drawn (Fig. 2).
165
D. M. ANDERSON Fig.
1.
PS9
l l
r
t
1Q.g7.*c-------2 -0
-----
go*
l
.g
0.95
k cJ
F
l l
3 al i
l
l
2
--------
1SD,_ _
-----------_ l
0
l
MEAN
l _
3-e)
-*-
-
-
-
-
-
l
l
_
-
_
-
-
_
_
LS.0.
_
_
l 0.93
l
-
t 0.91
i 25
30
HaemZxrit
35
45
55
50
(%) The relation
between
“F”
and haematocrit.
The mean
and the S.D. are shown.
Fig. 2.
0.99
l
f
l
LG.97----
--------
3
-
3-
- - - -
l
l
-
-
-
_
-
-‘shoe-
_
l
l l
2 LL
MEAN l
,s
-
0’95
-
&ALL
AGES
l
l
l 8
-e _-------_-
E
&-------a-
-------
‘s.DLl
k
u
0.93
-
0.91
i I
I
I
30
10
50
Age in days ‘The relation
between
“F”
and the age of the pig.
The mean
of all ages and the S.D. areshown.
70
166
TRAPPED
PLASMA
CORRECTION
FACTOR
IN
PORCINE
BLOOD
There was little difference in the haematocrit of the same blood sample measured by Wintrobe and ‘Lmicro” methods. In Table 1 a comparison of lilt. results obtained by the two methods is shown. The mean “micro” haematocrit M as 32.87 + S.E. 1.19 and the mean Wintrobe haematocrit (3,000 s for 30 minutes) was 33.26 rt S.E. 1.14. This difference was not significant. The age of the pig did not affect the agreement between the haematocrits derived by the t\vo methods.
TABLE THE
Microhaernntocrit
24.1 25.3 27.7 35.8
33.4 37.4 33.4 38.9
33.7
1
HAEMATOCRIT (%) OF SAMPLES OF PIG BLOOD AS DETERMINED MICROHAEMATOCRIT METHOD OR WNTROBE TUBES
Wintrobe
Microhaemotocnt
24.3 25.3 29.5 36.1 34.4 37-5 34.0 39.2 34.3
BY THE
IVintrobe
31.2
33.0
34,a
34.8 28.4
27.7 25.1
34.4 33.6 35.0
2.54 34.4 33.7 35.0
38.1
38.2
41.1
41.2
In the determination of Wintrobe haematocrits the time during which the samples were centrifuged appeared to have little effect. In the set of samples mentioned in the previous paragraph the mean Wintrobe haematocrit after 15 minutes at 3,000 x g was 34.0 per cent., after 30 minutes 33.26 per cent. and after 60 minutes 33.13 per cent. The difference between the 15 and 30 minute estimates just failed to reach significance (0.05 < P < O*l), while there was no significant difference between the values obtained after 30 and 60 minutes treatment. DISCUSSION
The most striking point about the results obtained in the present experiments in the lack of correlation between the amount of trapped plasma and the haematocrit. Such a correlation has been demonstrated in the blood of the sheep and of man (Chaplin and Mollison, 1952) and is considered to result from the decrease in the mean relative centrifugal force (RCF) applied to the red cell column as the length of the column increases towards the axis of the centrifuge. This result has most often been demonstrated using a large number of samples of blood of varying haematocrit which have been made up from less than five large blood samples. In this way all variables which affect trapped plasma except hacrnatocrit have been kept to a minimum. When this was done in pig blood no correlation between trapped plasma and haematocrit could be demonstrated. In fact in such experiments the amount of trapped plasma was extremely constant; when the haematocrit of one sample was altered to 28.2 per cent., 37.3 per cent. and 48.2 per cent., the values of ‘F’ were O-963, 0.955 and 0.958 respectively. The most likely explanation is that the combinations of RCF and time used in the present experiments to determine Wintrobe haematocrit were such that the
D.
M.
ANDERSON
167
decreases in RCF brought about by different lengths of red cell column were not important. Obviously this must be the case using the ‘micro’ technique with the blood of all species, since the length of the red cell column is not constant in replicates of the same blood sample, yet the method is very repeatable. The reason for the ease with which minimum values of trapped plasma were obtained using Wintrobe tubes may be related to the marked tendency towards rouleaux formation and high sedimentation rates exhibited by pig erythrocytes (Schalm, 1961). Thus, compared with sheep blood which does not readily form rouleaux, the centrifugal force applied to the red cells in pig blood will be greater at a constant angular velocity and radius because of the greater mass of the rouleaux as compared with individual red cells. The tendency to form rouleaux will not however have any effect on the final degreee of packing achieved (Ponder, 1952). The possibility was also considered that, since RCF is a function of both the radius and the speed of rotation of the centrifuge, then in the centrifuge used in the present experiments, the alteration in mean RCF brought about by changes in the mean length of the red cell column in the Wintrobe tubes was less then in other designs of centrifuge. It is possible, however, to calculate that in the centrifuge used in the present experiments which achieved 2,950 x g at 3,800 rpm., the mean RCF in the red cell column dropped from 2,747 i: g at a haematocrit of 26 per cent. to 2,585 x g at haematocrit 46 per cent., a drop of 5.9 per cent. In the centrifuge used by Hodgetts (1959) which achieved 3,044 x g at 4,000 rpm. a similar change in haematocrit lowered mean RCF from 2,811 x g to 2,632 x g> a drop of 6.4 per cent. ‘The drop in mean RCF was, therefore, of the same order in both cases but it is apparent that correcting equations as suggested by Hodgetts f 1959), apph. only to haematocrit derived in a centrifuge of the same radius. It appears, therefore, that minimum \.alues of trapped plasma are readily achieved in samples of pig blood, even at relatively low centrifugal forces. Ho\ve\ cr, once the amount of trapped plasma has been reduced to the levels shown in Fig. 1 no amount of additional treatment will reduce the amount. This is in direct contrast to the results obtained with human blood by Jackson and Nutt (195 I) who reported that centrifugation in excess of 4,000 x g for 15 minutes reduced trapped plasma almost to zero. Leeson and Reeve (195 1) suggested on theoretical grounds that to obtain less than 9 per cent. trapped plasma some deformation of the erythrocytcs must take place. The present results however agree with the statement by Ponder (1952) that when red cells are ‘more than about 95 per cent. packed, relativrly tremendous forces are required to pack them further.’
SUMMARY
The trapped plasma correction factor in centrifuged samples of pig blood was 0.955 f 0.015 (S.D.) M’ mrmum * values of trapped plasma were quickly achieved using both high and low centrifugal forces. There was no relation between the amount of trapped plasma and the haematocrit of the sample. The age of the pig from which the blood sample was obtained did not affect the amount of trapped plasn la.
168
TRAPPED
PLASMA
CORRECTION
FACTOR
IN
PORCINB
RI.OOD
REFERENCES
Chaplin, H., and Mollison, P. L. (1952). Blood, 1, 1227. Dunne, H. W. (1964). Diseases of Swine. 2nd Ed. Iowa State University Press; :\mes, Iowa. Gregersen, M. I., and Rawson, R. (1959). Physiol. Revs. 39, 307. Hlad, C. J., and Holmes, J. H. (1953). J. up@. Physiol, 5, 457. Hodgetts, V. Elizabeth (1959). Ausr. J. exp. Biol Med. Sci., 37, 97. Jackson, M. D., and Nutt, M. E. (1951). J. Physiol. Lond., 115, 197. Keith, H. M., Rowantree, L. G., and Geraghty, J. T. (1915). Arch. int. Med., 16, 517. Leeson, D., and Reeve, E. B. (1951). J. Physiol. Lond., 115, 129. Owen, C. A., and Powers, M. H. (1953). J. appl. Physiol., 5, 323. Ponder, E. (1952). Haemolysis and Related Phenomena, J. and A. Churchill; London. Schalm, 0. W. (1961). Veterinary Haematology, Bailliere, Tindall and Cox; London. Talbot, R. B., and Swenson, M. J. (1963). Amer. J. vet. Res., 24, 467. [Received
for publication,
june
12th, 19691