31
tubes are required-for each specimen of serum and two for controls, A convenient size to use is
10 c.m. long and 12 mm. wide. The tubds are carefully washed in distilled water, dried,
numbered and arranged in a rack 1, 2, 1A, 1B, 2A, 2B, 3A, 3B, 4A, 413, etc. Into each
tube is put 1·5 cc. distilled water. To each of tubes 1 and 2, the controls, 50 c.mm. of ·85 per
cent. NaCI is .then added. To each of LA and 1B is next added 50 c.mm. of one of the serums, to
each of 2A and 2B 50 mum, of another of the serums and so on. Then one drop of a 5 per cent.
solution of pot. chromate is added to every tube as indicator, and. the contents are evenly mixed
by shaking. A standard solution containing ·2906 per cent. silver nitrate having been prepared
previously, 420 c.mm, of this are dropped from a calibrated pipette fitted with a rubber teat into
control tube 1. The yellow colour remains unchanged, 440 c.mm. are next dropped . into control
tube 2. This amount suffices to combine with the whole of the chloride present and to leave
. sufficient excess to give a distinct brownish tint of silver chromate in suspension, The silver
nitrate solution is next dropped into each of the serum tubes in succession until, by comparison
with control tube 1 in which the reaction is incomplete and control tube 2 in which it is complete,
it can easily be judged when the end point has been reached. Tubes A and B of each serum
serve to control each other. 280 c.mm, of silver nitrate may be added to each serum tube to begin
with and then successive amounts of 10 c.mm., shaking well between each addition, until the right
degree of brown colouration remains permanent. It is advisable to keep all the tubes, especially
the controls, shaded from direct light until the estimations have been finished, for the precipitate
of silver chloride rapidly blackens in the light and renders accurate judgment more difficult.
Trials were made to ascertain what excess quantity of silver nitrate was required to give a
definite brown tint in a chloride solution of known strength. Theoretically 50 c.mm. of ·85 per
cent. NaCl require 422 c.mm. of the standard AgNO3 solution for the completion of the
reaction, and any excess quantity of silver goes to form red silver chromate with the indicator.
In practice it was found that not until nearly 440 c.mm, of the silver solution had been added
was the brown tint sufficiently marked to be judged by the eye. Therefore in calculating the
percentage of chlorides in the serum 15 c.mm was always d e d u c t e d f i r s t f r o m t h e q u a n t i t y u s e d ,
since this amount was required to give the visible colouration. Even then the method gives a
higher scale of chlorides than is obtained by the incineration method. This, however, does not
matter for comparative purposes since the results given by our method showed a remarkable
degree of uniformity from day to day. For example we put up several specimens of a serum
from a horse, and another from a rabbit in 'sealed pipettes and tested one of these from time to
time along with the human serums. The percentage worked out to ·63 per cent. or ·635 per cent.
chloride in each of the specimens of horse serum and to ·68 per cent. or ·685 per cent. in each of
the specimens of rabbit serum, that is to say an error only appeared in the third place of decimals.
In working rapidly it might be possible to make an error of one above or one below in the second
place of decimals, and we believe that to be the extreme limit of the possible experimental error of
the method, always assuming that the operator has practised it a few days and works with care.
This work was undertaken with the object of ascertaining whether any alteration in the
chloride content of the serum of patients undergoing the antirabic treatment in vogue at this
Institute occurs. Harvey and McKendrick (36) working at the Kasauli Pasteur Institute showed
by their method that patients treated according to Pasteur's system with dried, cords incurred
a reduction in the percentage of chlorides in their serum, but that patients treated with fresh
medulla diluted according to Hogyes' system did not incur a reduction to a similar degree.
After some trial of Harvey and McKendrick's chloride estimation method in watch glasses
we abandoned it as it seemed more difficult and less accurate, and devised the test tube method
described above,
To obtain a standard for comparison we examined the serums of 48 healthy persons of
various races with the following results:—
TABLE NO 18.
Race.
Diet.
Number
of
individuals,
Percentage of chlorides.
Maximum.
Minimum.
Mean.
Europeans ...
... Mixed ...
,,.
13
· 6 9
· 6 0
· 6 3 2
Hindus
...
... Rice ...
...
8
· 6 7
· 6 3
· 648
Hindus
,..
... Ragi
...
8
· 6 8
· 6 1
· 6 4 6
Hindus
...
... Mixed ..,
...
13
· 6 7
· 6 1
· 6 1 6
Musalmans .
... Mixed ...
...
6
· 6 6
· 6 0
· 6 3 3
Total ...
48
· 6 7 m e a n
maximum.
· 6 1 m e a n
minimum.
· 641 mean of
total.
9