8
whose origin was unknown to me, but known to the sender, which is given on
pages 18-20, shows this. Weichardt1 had suggested that the "side-action" of an
antiserum should be removed, by exhausting its power to cause this, as is done
by the absorption-method with such success when allied bacteria are being
differentiated. It appears to me that this method of dealing with an antiserum
is not suitable for medico-legal work in India: the following experiments go far
to show that the modification of the antiserum which is desired cannot always be
obtained. An anti-ovine serum reacted well with a 1-1000 dilution of sheep's
serum, and faintly with a similar dilution of goat's serum: to 1 c.c. of the anti-
serum was added 0,07 c.c. of goat's serum, and the mixture, after being thorough-
ly shaken, was left in the ice-chest overnight, and centrifugalised next morning,
the supernatant fluid being decanted and tested. It was found that the reaction-
power with goat's serum was no longer present, but the power of reacting with
sheep's serum in 1-1000 dilution had also been lost—the modified antiserum was
now useless for medico-legal work. Again, an anti-hircine serum that gave a
good reaction with a 1-3000 dilution of its antigen, and a less rapid and less
marked reaction with a similar dilution of sheep's serum, was treated with sheep's
serum in the proportions noted above and shaken, kept on ice, and centrifugalised
as described. The resulting fluid was found to be incapable of reacting with a
1 - 1 0 0 0 d i l u t i o n o f s h e e p ' s s e r u m , i t i s t r u e , b u t , a s i t h a d a l s o l o s t i t s p o w e r o f
reacting with a 1-1000 dilution of its antigen, it had become useless.
Supposing that either of these modified antisera had been stored and used,
without preliminary testing of their powers, on the strength of the recommenda-
tion made by so competent an observer as Weichardt, then, in a case in which a
faint "ruminant reaction" had been 'obtained one might have been led to conclude
that neither goat's nor sheep's blood was present in the stain, when in point of
fact either might be present, for all that one could say. Jurare in verba
magistri is a recognised good practice in matters legal; in matters medical it
is a fruitful source of error.
The precipitate produced by the inter-reaction of a precipitin-antiserum and
its antigen is soluble in excess of either antiserum or antigen,, a fact which goes
far to prove that the necessary condition of precipitation, besides a certain
salt-content of the medium, is a change in the electric charge of the colloid parti-
cles held in suspension in the inter-reacting fluids. This fact Dehne has tried to
utilise as a confirmation of the results obtained by the precipitin test. He
r e c o mme n d e d 2 t h a t , wh e n a p r e c i p i t a t e h a d b e e n o b t a i n e d , t h e r e s h o u l d b e
1 WEICHARDT:—Der Nachweis individueller Blutdifferenzen. Hyg. Rundschau, 1903, xiii, 756.
Zur Frage des Nachweises individueller Blutdifferenzen. Vierteljahrschr. f. ger. Med. 1905, xxix. 19.
2 DEHNE.—Die spezifische Löslichkeit und ihre Anwendung bei der forensischen Blutuntersuchung.
Münchener med. Wochenschr. 1907, 357.