Sources of Error 81 



NaOH 



Strangeways has made numerous observations (unpublished) on the 

 differences in precipitum-forming power of the sera in disease." 



We have found that an acid-reacting blood dilution will because 

 of the acidity alone produce precipitation (see below and Section IX.). 

 The observation has considerable practical importance medico-legally, for 

 the reason that blood stains may occur on acid fabrics, or acid-reacting 

 leather, the acidity in the substratum impeding the test by the anti- 

 serum in the blood solution made by steeping the stained article in 

 saline solution. The subject has been carefully gone into by Graham- 

 Smith and Sanger (p. 281), who report as follows : 



" Observations on the reaction to litmus of extracts of coarse cloths 

 and leather, as well as the possibility of the treatment of blood-stains in 

 forensic practice with chemical reagents, made it desirable to investigate 

 the action of such reagents on blood. 



Acids. 



Several experiments were made with dilutions of both organic and 

 inorganic acids in distilled water and salt solution. Dilutions from 

 1 in 10 to 1 in 100,000 were tested by dropping in serum and noting 

 the effects up to 2 hours and after standing for 24 hours. In these 

 observations one drop of antiserum was added to about '5 c.c. of the 

 dilution since this has been the quantity uniformly used in qualitative 

 work. 



The addition of larger quantities produced slightly different results, 

 probably owing to the alkalinity of the serum itself, and moreover, 

 perhaps for the same reason, the effects of different sera were noticed to 

 vary slightly. This remark applies to all the following experiments of 

 a similar nature. 



With the inorganic acids a noteworthy phenomenon was observed. 

 Strong solutions (1 in 10) in salt solution caused coagulation of the 

 serum and destruction of the precipitating substance, whereas weak- 

 solutions (1 in 100) produced no result. Dilution between 1 — 500 and 

 1 in 10,000 caused more or less clouding, in the latter case taking place 

 half-way up the tube. These cloudings probably resulted from the 

 N. 6 



