NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
122
In order to see whether this effect, clearly demonstrated upon dogs, was of
general application, we used another species of animal, namely, rabbits. As we had
not at hand a specific serum hæmolytic for rabbits blood we utilised (1) daboia
venom, (2) cobra venom lecithid. The results of these experiments in regard to
the isotonic point were as follows :—
Experiments with daboia venom.
Rabbit I .—Weight 3 lbs.
4 P.M. Received 50 m. grrns. dried daboia venom in solution
.
6 P.M. Animal breathing rapidly. Cyanosis of ears.
9 P M. Animal died.
ISOTONIC POINT.
.91 %
.83 %
.17 %
.62 %
.52 %
.45 %
.4 %
4. P.M.
..
..
. .
0
0
trace
hh
complete
6. P.M.
..
..
..
0
0
marked
nearly corn-
plete.
complete
9. P.M.
..
0
0
nearly corn-
plete.
nearly corn-
plete.
. .
. .
. .
No hæmoglobinuria.
Rabbit II .—Weight 2½ lbs.
8-30 A.M. Received 25 m. grms. dried daboia venom in solution.
11 A.M. Died.
ISOTONIC POINT.
.62 %
.52%
.45%
.425%
.4%
8. A.M.
..
..
..
. .
. .
. .
0
h
nearly com-
plete.
11 A. M. (just before death)
. .
0
marked
nearly com-
plete.
nearly com-
plete.
nearly com-
plete.
No hæmoglobinuria.
Rabbit III.—Weight 2½ lbs.
8-30 A.M. Received 10 m. grms, dried daboia venom in solution.
11 P.M. Died.
123
ISOTONIC POINT.
.82%
.71 %
.62 %
.52 %
.45 %
.425%
.4%
8 A.M.
..
0
0
0
0
0
tr.
nearly com-p l e t e .
4 P.M.
..
0
tr.
nearly com-
plete.
nearly com-
plete.
nearly com-
plete.
..
. .
No hæmoglobinuria.
Experiments with cobra venom lecithid.
Rabbit No. 1.—Weight 3 lbs. At 8-30 A. M. .01 grms. cobra.
At 4 P.M, .15 „ lecithid.
No noticeable effect produced upon the animal.
I S O T O N I C P O I N T .
.71 %
.62 %
.52 %
.45 %
.4 %
12 A.M.
..
..
..
. .
0
0 tr.
h
complete.
4 P.M.
..
..
..
. .
0
0
0
tr.
complete.
9 P.M.
..
..
..
. .
0
0
0
0
nearly com-
plete.
Rabbit No. 2.—Weight 2½ lbs. At 8-30 A.M. .03 grm. cobra-lecithid.
At 4 P. M. .3 grm.
Animal showed no ill effects.
ISOTONIC POINT.
.71 %
.62 %
.52 %
.45 %
.4 %
12 A. M.
..
..
..
. .
. .
0
0
tr
complete.
4 P. M.
..
..
..
. .
. .
0
h
hh
complete.
9 P. M.
..
..
..
. .
. .
0
0
0
nearly com-
plete.
The raising of the isotonic point seems therefore to be a frequent concomitant
©r result of specific hæmotoxic action on the red cells. The absence of any change
in the case of the non-toxic cobra venom lecithid we shall refer to in Part IV.
124
An important deduction to be made from these results is that, if a raised
isotonic point be shown in Black-water Fever, it would not necessarily show lysæmia
to be the result of changes in the osmotic relations of the plasma and corpuscles,
but it would be presumptive evidence of the presence of a hæmotoxin.
IV.-RELATION OF ISOTONIC POINT TO LYSÆMIA.
It has been noticed that by the injection of specific serum or snake venom,
the isotonic point of the red corpuscles is raised in varying degree. It must also
be remarked that when this raising of the isotonic point had reached a certain
value, i.e., about 9 per cent. salt solution, hæmoglobinuria resulted ; so long
however as the isotonic point remained below this, animals exhibited neither
hæmoglobinæmia nor hæmoglobinuria.
Several estimations gave the hæmosozic value in dogs at about equal to
9 per cent. to 1 per cent. salt solution. It seemed therefore possible that, in these
experiments, lysæmia was the result of the solution of red cells whose power of
resistance to hypotonic salt solution was nil, and occurred at the time when the
isotonic paint had reached the hæmosozic value of the plasma.
Another interesting point in regard to the isotonic changes in experimental
hæmoglobinuria is seen in animals that have recovered from the effects of
hæmolytic serum. In such cases the actual isotonic point, i.e., the salt solution, just
insufficiently weak to cause any hæmolysis, remains high for two or three days,
whilst the amount of hæmolysis in the upper tubes of the series becomes less and
less, so that before any considerable laking takes place one has to descend nearly
to the normal salt value. Finally quite suddenly one day the slight hæmolysis
seen in the upper tubes disappears. In such cases it is easy to see that the
p h e n o me n o n i , d u e t o t h e e x i s t e n c e o f t wo t y p e s o f r e d c e l l s ; a d i mi n i s h i n g n u mb e r
of dark small corpuscles and an increasing number of large and more or less poly
– c h r o m a t i c c e l l s . W i t h t h e d i s a p p e a r a n c e o f t h e f o r m e r t h e i s o t o n i c p o i n t o f t h e
blood returns to normal or nearly so (vide dog VII).
These experiments show that the large polychromatic cells are not degenerat-
ed corpuscles, but the newly formed ones.
Their appearance seems therefore a phenomenon exactly similar to the out-
put of polychromatic and large cells after an attack of Black-water Fever.
It is not difficult to understand that the slight decrease noted by us as
sometimes seen in the isotonic point of Black-water Fever blood may be due
to this outpouring of new corpuscles into the circulation, rather than to the more
resistant cells having been left untouched by the blood destroying process, the
explanation usually offered.
125
No such association of lysæmia with the isotonic point seems to be present
in Black-water Fever, in which disease there is as we shall see no obvious change
or variation in the isotonic point during hæmoglobinuria.
V.—CHANGES IN THE RED CELLS.
Though marked anæmia was evident even to the naked eye, examination
of the blood showed very little change in the red cells,until with recovery there
was an outpouring of polychromatic and very large corpuscles.
In the viscera much more noticeable changes were seen ; very characteristic
was the marked contrast between very small and very large cells. In stained
preparations the former appeared as small dark very round cells (spherocytes),
the latter either polychromatic or very much larger than normal.
In dog No. VII as recovery took place the small cells disappeared giving
place to a remarkable influx of large and polychromatic cells. That these latter
were newly formed corpuscles seems undoubted, and the presence of similar cells
during convalescence from Black-water Fever has already been commented on.
When hæmoglobinuria is in progress shoals of ghosts or shadows are seen in
the renal and hepatic veins, but they are not conspicuous in films from the
peripheral blood. Where agglutination occurs as in the hepatic vein blood, the
groups of agglutinated cells are all spherocytes. These are often grouped about
one or two leucocytes. The larger cells lie on the outskirts of the cluster or
quite free in the spaces.
227 H. D.
21227 IL D.
127
CHAPTER IV.
THE LYSÆMTA OF BLACK-WATER FEVER.
The facts we have brought forward throw a good deal of light upon the nature
of the Black-water Fever process. It becomes evident that it is not the mere
amount of blood destruction but the nature of the process that is the fundamental
actor in the causation of the hæmoglobinuria of Black-water Fever. Viewed
in this light it is no longer difficult to see why in the severest attacks of malaria,
although blood destruction may be very great, hæmoglobinuria does not result.
The loss of red cells in an acute initial attack of malaria may amount according
to Kelsch (73) to 1,000,000 per c.m. in one day, and Dionisi (73) has observed a fall
of 500,000 per c.m. in twelve hours ; yet these cases showed no hæmoglobinuria.
On the other hand cases of hæmoglobinuria have been observed in which the maxi-
mum loss of red cells amounted only to 129,000 per c.m. (Bristowe and Copeman).
In malaria we have an example of what we have termed " erythro-katalysis " ; in
Black-water Fever the process is essentially a lysæmia.
In malignant tertian malaria some of the most noticeable features of the
condition are—( a) the tendency to accumulation of infected corpuscles in the
visceral capillaries, ( b) the excessive rarity of sporulating bodies in the peripheral
circulation, and ( c) the frequently recorded marked alteration in the infected red
cells and active engulfment of these by phagocytes. All these peculiarities are
evidently due to the specially pronounced action of the malignant tertian parasite
in bringing about erythro-katalysis.
In quartan and benign tertian malaria on the other hand there is not the same
tendency for infected red cells to be held. up in the visceral capillaries, segmenting
parasites, especially in the case of quartan infection, appear very frequently in the
peripheral circulation, and phagocytosis of infected red cells is so rare that Thayer
states that he has never observed it. From such considerations we should judge
that the quartan parasite had an effect even feebler than that of the benign tertian
parasite in bringing the infected corpuscle to the state in which it becomes subject
to erythro-katalysis.
In pernicious anæmia according to Hunter there is solution of red cells in the
portal circulation, due to the action of hæmolytic substances absorbed from the
gastro-intestinal tract ; in other words a portal lysæmia takes place. Whether in
Black-water Fever the lysæmia occurs in the portal vein, but in such large amount
as to produce general hæmoglobinæmia ; or whether the hepatic or peripheral cir-
culation forms the site of the process we do not know.
128
It still remains for us to ascertain, if possible, the actual nature of the lysæmia
of Black-water Fever, whether it is due to change in. the osmotic relations, chemico-
toxic bodies, or to the production within the body of some specific hæmolysin.
BLACK-WATER FEVER NOT DUE TO CHANGES IN OSMOTIC RELATIONS OF THE RED
CELLS AND PLASMA.
Hamburger (73) , Von Limbeck (80), and others have studied the behaviour of
red blood corpuscles in salt solutions of different strengths. If blood corpuscles
be placed in salt solutions weaker than the plasma in which they have been bathed
they do not necessarily become destroyed ; only when the salt solution is consider-
ably weaker than the plasma does this happen. Human serum, which for all
practical purposes in this connection, may be considered as approximately repre-
senting the condition of the plasma, is estimated to have an osmotic tension equal
to .9 per cent. sodium chloride solution (Hamburger). But human red cells become
hæmolysed only when a salt solution below about .46 per cent. salt solution is so
used. Such a percentage which is just above the strength of solution necessary
to cause laking has been called the " Isotonic point."
It will be obvious that the isotonic point in itself represents no re al quality
but measures only one kind of resistance of the red cell, the limit of its power to
resist want of osmotic relation between its own substance and the plasma.
This resistance is we have just seen so great that for hæmolysis to take place
in the body by a reduction in the osmotic tension of the plasma would require,
provided the isotonic point remained the same, a reduction of the salt content
of the plasma to one-half or more of the normal. This fact explains why under
normal circumstances an equal volume of distilled water added to one of blood
does not result in marked laking, and also makes it evident that enormous reduc-
tions in the salt content of the plasma may take place without any danger of
hæmolysis.
But if the power of the red cells to resist laking vary, as indicated by the
isotonic point, so that they can stand less osmotic strain, then so much the more
is reduction in the salt content of the plasma likely to lead to hæmolysis. In
investigating the condition of the blood in Black-water Fever It is necessary there-
fore to consider both corpuscles and plasma, and to estimate both the isotonic point
on the one hand, and the hæmosozic value (osmotic tension of plasma) on the
other.
Isotonic point,—In, our observations we have estimated the isotonic point by
adding measured quantities of blood (10 to 20 c.m.) to known quantities of salt
solutions (.5 or I c,c.) of various strengths, shaking, allowing to stand for a few
129
moments, and centrifuging. It is well known that all the blood cells are not
of equal isotonicity so that a considerably weaker salt solution is required to
produce complete or nearly complete hæmolysis than to show a' tint due to
solution of the few less resistant corpuscles. In our experiments using fused
sodium chloride the first trace of laking in, normal blood was generally distinctly
visible in a N/13 salt solution, equal to . 449 per cent. A quite distinct colour
was given at N/14 or .417 per cent., and as a rule marked but still incomplete
hæmolysis at N/15o r N / 1 6 E s t i m a t e s o f t h e p e r c e n t a g e o f h æ m o g l o b i n s e t f r e e a t
each dilution of the series were made by comparison with standards, prepared
with known precentages of the blood in, distilled water.
With slight variations they usually showed as follows :—
N/12
N/13
N / 1 4
N/15
N/16
Nil.
Nil.
5 to 10 per cent.
15 to 30 per cent. 40 to 50 per
cent.
In later observations we used a regular series of percentage solutions varying
by .025 per cent. These allowed greater accuracy than normal solutions in which
the intervals towards the lower end of the scale are far too wide. Subsequently we
adopted for convenience in preparation a series of dilutions prepared from a 10 per
cent. solution of sodium chloride.
Every case upon which we have based conclusions has been contrasted with one
or more control bloods, and we have also frequently repeated our observations in
regard to the more critical points. In Black-water Fever a difficulty is introduced
by the intense yellow colour of the serum, and the presence of hæmoglobinæmia
giving a tint in all tubes independently of any laking by the salt solution. The
anæmia too renders the tints obtained not comparable with those from normal blood,
but this difficulty refers only to the amount of hæmolysis in the different tubes ; in
ascertaining the limit of hæmolysis (isotonic point) and the main facts regarding
the behaviour of the blood to salt solutions it does not interfere. A rough allowance
for the anæmia was made by comparing the patients blood with normal in given
volumes of distilled water.
As regards the tint due to the colour of the plasma in Black- . water Fever, this
was allowed for by considering the first increase of tint observed in the series of tu
b e s
a s e q u i v a l e n t t o t h a t p r o d u c e d b y N / 1 4 s a l t s o l u t i o n o n n o r m a l b l o o d .
227H D.
2K
130
The isotonic point in Black-water Fever.—Marked changes in the isotonic point
have never been found by us in Black-water Fever. By marked changes we refer
to such changes as have been given in our animal experiments where from about
. 5 p e r c e n t . t h e i s o t o n i c p o i n t h a s b e e n r a i s e dt
o . 7
p e r c e n t . ,
. 8 p e r c e n t . a n d
even . 9 per cent . ; when. i t s det er mi nat i on becomes obscur ed by t he exi st ence of
hæmoglobinæmia. In Black-water Fever then our researches have . been con-
fined to the recording of comparatively minute variations which it must be con-
fessed cannot be considered as affording any appreciable support to the idea
that the hæmolysis in this disease has any relation to osmotic variations in the
plasma, though they may indicate, as we have seen, the action of hæmo-toxins.
Our observations in this connection on Black-water Fever cases are as
f ollows :—*
Isotonic point of Black-water Fcver.
Percentage of salt
N
/12
N / 1 3
N
/14
N
/15
N
/16
N / 1 7
Case XVII
.. Four days after onset..
..
. .
..
tr.
hh
inc H
Case XVIII
.. Five days after onset..
..
Nil
tr.
tr.
h
hh
Case XIX
.. Day after onset. Mild case.
Hæmoglobinuria over.
Nil
Nil
h
inc H
. .
. .
Case XX ..
..
Day of onset.Hburia. tint
tint
incr-tint inc H
. .
. .
„
„
..
..
Day after onset. Hburia
..
incr-tint, incr-tint inc H
. .
. .
„
„
..
..
2nd day.Hburia.. tint
tint
h
hh
15%
inc H
40%
. .
,,
,,
..
. .
3rd day.6 hours after ces-
sation.Hburia.
Nil
Nil
h
hh
inc H
.
Percentage of salt..
. 525
.5
.475
.45
.425
.4
Case XXI
.. 6 hours after onset. Severe
case.
tint
tint
tint
tint
incr-tint inc H
Case XXVI
.. Day after onset.Hburia
tint
tint
tint
tint
tint
incr-tint
Control
..
..
....
Nil
Nil
Nil
Nil
tr.
h
Percentage of salt..
.476
.454
.434
.416
.4
.384
Case XXVII
.. Day after onset.... tint
tint
incr-tint incr-tint inc H
..
,,
,,
..
2nd day.Hburia.. tint
tint
tint
incr-tint inc H
. . .
Control
_
..
....
Nil
Nil
Nil
h
hh
Inc H
* NOTE- Vide footnote on page 118,
131
Again in cases of malaria we have sometimes seen small variations which may,
or may not, have significance in so far as they demonstrate the action of this disease
on the blood. Of large variations at all likely to lead to hæmolysis in a condition
of even markedly lowered strength of the plasma we have no evidence. In such
persons whom we judge to be possible subjects of Black-water Fever in the near
future, again we find only changes of extremely small degree. These facts will be
clear from the following list of observations :-
Isotonic point of Europeans resident in the Duars.
Series 1.
Percentage of salt
N
/12
N
/13
N
/14
N/15
N
/16
N
/17
New-comer
.. Has had no malaria for
many years.Control I.
N i l
tr.
h
inc H
inc H
. .
New-corner
.. Has had no malaria for a long
period.Taking quinine
5 grs. daily.Control 2.
Nil
tr.
h
inc H
inc H
. .
Old resident.. 20 years in the Duars..
N i l
Nil
tr.
hh
inc H
. .
Resident..
5 years in the Duars..
Nil
tr.
h
inc H
. . .
. .
”
” ” ” ”
Nil
Nil
h
inc H
. .
. .
”
” ” ” ”..
Nil
tr.
h
inc H
. .
. .
”
2 years in the Duars
suffering much from fever.
Anæmic.
Heterogeneity
of corpuscles marked.
Nil
tr.
h
inc H
. .
. .
”
1 year.Much fever..
Nil
Nil
h
h
. .
. .
Series 2.
Old resident.. After fatiguing journey..
tr.
h
hh
inc H
. .
. .
” ”
Next morning. 10 grs.
quinine the previous night.
Nil
Nil
tr.
h
hh
. .
” ” . . Jalpaiguri. Healthy condi-
tions.
Nil
Nil
Nil
tr.
h
. .
Control 2 ....
. . . .
N i l
.Nil
Nil
Nil
tr.
. .
132
Isotonic point of Europeans resident in the Duars. —(contd.).
Percentage of salt.
N
/12
N
/13
N
/14
N
/15
N
/16
N
/17
Percentage of salt ..
..
.476
.454
.434
.416
.4
.384
Series 3 .
Resident ..
. . 2 years in the Duars
Nil
Nil
tr.
h
hh
..
„ . .
. . 6 months. Much fever .. Nil
Nil
Nil
tr.
h
. .
„ . .
. . 6 years
..
. . . . Nil
Nil
tr.
hh
inc H
..
Old resident
. . Had Black-water Fever
one year ago.
Nil
Nil
tr.
h
inc H
..
Control I
. . Some hours before onset of
malaria.
Nil
tr.
h
hh
inc H
..
Resident ..
.. 6 months ; taking quinine 5
grs. daily.
Nil
Nil
Nil
tr.
..
..
Old resident
.. Many years in the Duars .. Nil
tr.
h
hh
..
. .
Isotonic point of Bengali Babus resident in the Duars.
Percentage of salt
..
..
.475 .45
.425
.4
.375
Series 1.
Bengali Babu .. 6 months' resident. Enlarged
spleen. 70 per cent. Hb.
Nil
tr.
h
inc H
..
„
„ .. 6 months' resident. 95 per
cent. Hb.
Nil
tr.
h
hh
. .
„
„ .. 4 years' resident. 75 per cent.
Hb.
tr.
h
hh
inc H
. .
„
„ .. Numerous M. T. rings, cres-
cents. Enlarged spleen. 80 per
cent. Hb.
Nil
Nil
tr.
h
. .
„
„ .. Many years' resident
.. Nil
Nil
tr.
h
..
„
„
. .
„
„ „
.. Nil
Nil
h
hh
. .
„
„ . .
„
„ „
..
Nil
Nil
Nil
tr.
. .
133
Isotonic point of servant class.
Percentage of salt
. .
. .
N/12
N / 1 3
N/14
N/15
N / 1 6
Madrassi ..
.. First attack of fever
..
tr.
tr.
h
inc H
. .
„
. .
. . Next morning. Fever till 5 A. M.
Benign tertian parasites. Had
10 grs. quinine previous
night.
Nil
tr.
h
inc H
. .
„
.. 5 days later
..
..
Nil
Nil
tr.
hh
. .
Control ..
..
. . . .
Nil
tr.
h
inc H
..
Percentage of salt ..
. .
. .
. 5 2 5
.5
. 4 7 5
. 4 5 .425
Marwari ..
.. 5 years in the Duars. Anæmic.
Spleen three inches below costal
margin.
Nil
tr.
tr.
hh inc H
Isotonic point of coolie class.
Percentage of salt
..
..
N / 1 2
N/13
N/14
N / 1 5
N / 1 6
Series
Coolie
. .
.. Fever. Benign tertian parasites
Nil
Nil
tr.
h
. .
„
.. Fever. M. T. infection ..
Nil
Nil
tr.
h
. .
Control I ..
. .
. . . .
Nil
tr.
h
inc H
. .
Coolie
..
.. Anæmia
..
. .
..
Nil
Nil
tr.
. .
. .
„
. . . .
Nil
Nil
tr.
. .
. .
Native child
.. 8 years old. Anæmia. Fever ..
Nil
Nil
tr.
..
. .
Percentage of salt
..
..
.475
. 4 5 .425
.4
.375
Series 2.
Jaundice. Serum bright yellow.
Bile in urine. A few M. T. rings.
Nil
Nil
Nil
Nil
tr.
Coolie
. .
.. Anæmia. Enlarged spleen Many
nucleated red cells.
Nil
Nil
Nil
tr.
. .
227 HD
2L
134
Isotonic point of coolie class.
Percentage of salt
. .
..
N / 1 2
N / 1 3
N / 1 4
N / 1 5
N
/ 1 6
Coolie
.. 1 year resident. Fever. Enlarged
spleen. Numerous S. T. rings.
Nil
Nil
Nil
Nil
tr.
„
. . 1 year resident. Quartan parasites Nil
tr.
h
hh
. .
„
. . Anæmia. Numerous S.T. parasites Nil
Nil
Nil
tr.
. .
Bhutia ..
..
. . . .
Nil
Nil
tr.
. .
..
Control 2
.. 1 month resident. S. T. parasites
Nil
Nil
tr.
hh
..
Coolie
..
.. Next day after 15 grs. quinine
Ni l
Nil
tr.
hh
..
„
. . . .
Nil
tr.
h
hh
..
Isotonic point after administration of quinine.
The following are observations upon the effect of the administration of qui-
nine sulphate upon the isotonic point:—
Normal person.
N / 1 2
N
/13
N / 1 4
N/15
N / 1 6
Immediately after taking quinine
. .
. .
Nil
tr.
h
inc H
. .
3 hours after administration of quinine sulph 15
grs. and dil sulph. acid m. 15.
Nil
Nil
h
inc H
. .
4 hours ditto
Nil
tr.
h
inc H
. .
Resident 5 years. Given 15 grs. quinine sulph. and m. 15 dil. acid. sulph.
N / 1 2
N / 1 3
N/14
N / 1 5
Immediately before taking quinine
. . ..
. .
Nil
tr.
6%
h
25%
inc H
40%
5 hours after administration
. . ..
. .
Nil
tr.
h
inc H
Next day
. .
. .
. .
. . ..
. .
..
tr.
12%
h
17%
inc H
50%
135
The action of quinine on the isotonic point, if it exists, is a small one that
can have no effect in regard to hæmolysis by osmotic variations.
Hœmosozic value—Hamburgher estimated the osmotic tension of the
plasma by adding small quantities of normal blood corpuscles to various dilu-
tions of the serum to be tested. Later Ruffer (82), Wright and Kelner (83),
Wright and Ross (84), McCay (48) and others have studied in greater detail
this value which Ruffer has named the “ Hæmosozic value ” of the serum.
Wright and Kelner’s method of estimating the hæmosozic value, which is
also used by McCay, is briefly as follows :—
In a number of capillary tubes a series is made by mixing I vol. of blood with
2 vols. of different salt solutions of greater and greater dilutions and noting at
which point hæmolysis takes place. The serum to be tested is then diluted until
one vol. blood plus 2 vols. of the diluted serum gives hæmolysis.
It is obvious that the serum diluted to the extent noted is supposed to act in
the same manner as the particular strength of salt solution determined in the
first estimation.
If for example :-
1 vol. blood+2 vol. N/30 alt just gives hæmolysis and I vol. blood + 2 vols. serum/diluted 5 time
just gives hæmolysis.
then serum/4 = same strength as N/30.
or Serum = 194.
4
i.e., the serum = 4 ( 194) or• 776 per cent. salt.
In practice there are a number of difficulties in getting accurate results.
1. Want of fixed point as index.—We have already noted that there is no
fixed value in regard to the point at which all red cells are hæmolysed.
Thus in N/14 or .417 per cent. the least resistant cells are already hæmolysed.
In N/18 or 324 per cent. there are still many cells undissolved, so that in ascertain-
ing the salt solution in which hæmolysis takes place no fixed point can be deter-
mined.
Wright makes use of a change in the colour of the blood as an indication, but
this represents no fixed point, because it can be shown by centrifuging that
hæmolysis has already commenced before any definite change in the tint of the
blood can be observed. McCay uses the point at which complete solution of all