1 6
v a l i d r e a s o n w h y i t s h o u l d n o t b e s o f o r n a t u r a l a m b o c e p t o r s a l s o . O n t h e o t h e r
hand the method will give indications, for instance in the case of horse serum.
Fresh horse serum by itself will not lyse man RBCs and has only a slight action
on guinea-pig RBCs, but when these RBCs, are sensitized in heated horse
serum, 74 parts serum to i part RBCs, lysis of both is obtained with guinea-pig
complement, showing that horse serum contains some sensitizer for man RBCs
as well as for guinea-pig RBCs but that horse complement for some reason
does not lyse the former.
Experiments were made to determine whether better results were obtained by
previous sensitization of RBCs in a heated immune serum, before adding them to
the lytic mixture, than by adding the immune serum directly to the mixture. To
secure exactly comparable quantitative results is by no means a simple matter. It
is probable that amboceptor is absorbed by sensitive RBCs at a rate inversely
proportional to its concentration in the RBCs and, therefore, it takes an infinite
time for a serum to be entirely freed from sensitizer. It is likewise probable that,
if amboceptor is available in a hæmolytic system, the avidity of the RBC substance
for it varies with the amount of union with complement which has taken place, i.e. ,
if a molecule of amboceptor has been put out of action by union with RBC and
complement, the remainder of that RBC will be more avid of amboceptor than it
would have been if merely the union of an amboceptor molecule had taken place
in the absence of complement. Hence it is possible that, even when equivalent
proportions of RBCs and sensitizer are used, there will be more amboceptor
available for the RBCs if the immune serum be present in the system than if the
RBCs had had to fix all the sensitizer they could within a limited time from a
similar quantity of serum.
On incubation of two such series lysis occurs much more rapidly in the RBCs
already sensitized for the reason that half the reaction, that is union of amboceptor,
has already taken place, but the final results are very much the same. The
differences noted in our experiments were so small and inconstant that they are
attributed to error.
(10) Bordet several years ago showed that when amboceptor is in excess
RBCs can absorb more than they actually require for complete lysis with the
minimum active dose of complement, and that a given quantity of serum will lyse
more RBCs when they are added simultaneously than when they are added in
successive amounts.
As deviation could not be demonstrated in the ordinary way with sheep
RBCs sensitized in our Goat B antisheep serum, we desired to find whether the
above held good in this particular case. It proved that when the sheep RBCs
were added altogether the time required for complete lysis was immensely
pro-longed when the quantity of RBCs was doubled.
FreshGoat B serum ...
...
...
. . .
. . .
. . .
. . .
. . .
...
1. 0
1 .0
1. 0
Sheep RBCs
. . . .
. . .
—
. . .
. . .
. . .
. . .
0. 4
o.6
0.8
Time required for complete lysis in minutes
. . .
6'
17'
53'
but when the sheep RBCs were added 0.2 cc at a time to the same
quantity of serum, waiting for complete lysis of each lot before the addition of the
next, the lysin was soon exhausted.
Fresh Goat B serum ......
...
...
..
...
1 .0
. . .
0 ' 2
Sheep RBCs ...
...
..
. -
. . .
0 '2
__
0 ' 2
Time required for complete lysis in minutes
. . .
... ...
...
4'
43'
3 hours
not
complete.