THE PRECIPITIN TEST FOR BLOOD. 83 



controls in the nse of this test, there are but few conditions likely 

 to be met with in forensic practice under which human blood 

 could not readily be differentiated from other bloods. 



The use of weak anti-sera, which require a period of about 

 twenty-four hours to exert their action, should certainly be con- 

 demned for medico-legal work. Not only may many bloods 

 react to an antiserum after such a lapse of time, but there is 

 danger of bacterial development. 



As normal blood dilutions possess an alkaline reaction, 

 several observations have been made by Graham- Smith and 

 Sanger* with various samples of leather which nearly always 

 gave acid reactions on solution, chamois leather being alkaline, 

 suede kid glove only slightly acid, and the coarser leathers very 

 decidedly acid. It was found that nearly all the solutions of 

 leather could be neutralised and the blood test satisfactorily 

 employed. The thick polished yellow leather, however, forms 

 an exception, as the solution is yellow in colour and extremely 

 acid; the colour deepens on the addition of alkali. It is there- 

 fore impossible to obtain the specific test for blood from a 

 stain allowed to dry on it. It is assumed that the mode of 

 preparation of such leathers produces conditions which destroy 

 the blood in contact with them. It is, however, just possible, 

 under favourable conditions, when the blood has been thickly 

 deposited on the surface, to scrape it off and obtain a positive 

 reaction. 



A series of experiments was also made to determine the 

 effects of boot-blacking and polish. Blood stains blackened over 

 were hard to detect on the boot, but by treatment (neutralisation 

 and filtration) clear solutions could be obtained, and yielded 

 well-marked reactions. Polish also made no difference to tht 

 test. Tannin saline solutions proved to have a very deleterious 

 action on serum, rendering the application of the test, when it 

 is present in large quantities, impossible. 



There is just one more important fact to which I wish to 

 refer: monkey blood gives similar reactions to human blood, 

 though less strongly marked, upon the addition of anti-human 

 serum, and it is possible that in some parts of South Africa 

 cases may occur in which it would be necessary for the expert 

 to prepare an anti-serum for the most prevalent genera or 

 species of monkeys belonging to such a region in order to 

 satisfy the Court of the presence or absence of monkey blood in 

 the suspected blood-stains forming the exhibits in a criminal 

 case. 



In a series of experiments carried out on materials from 

 Scotland Yard Museum by Graham-Smith and Sanger,! it 

 was found that blood one year old on a hatchet, and also thirty 



* Nuttall's "Blood Immunity and Relationship," p. 396; Journal of 

 Hygiene, vol. 3, No. 2. 



+ Nuttall's Precipitin tests, 1904. 



