74 The Precipitins: Methods 



2. Overpowerful and Weak Antisera. 



Powerful antisera have been of considerable use to me in my work, 

 and have led to my being able to establish more remote relationships, 

 especially amongst the mammalia, as I have shown in speaking of the 

 " mammalian reaction," They may however be a source of error in 

 medico-legal work, as has been pointed out by Uhlenhuth. When an 

 antiserum is so powerful as to produce a reaction in non-related bloods, 

 its action should be weakened by dilution with salt solution as suggested 

 by Uhlenhuth, Kister and Wolff, and Ewing. This lessens the amount 

 of antibody they contain, and by suitable dilution their strength may be 

 graded to suit requirements. Weak antisera may also be a source of 

 error through their reaction being delayed and bacterial develop- 

 ment (see below, § 7) occurring in the mixture of antiserum and blood 

 dilution. 



3. Suitable Dilution of Bloods tested. 



In view of the fact that concentrated dilutions of different bloods 

 may give reactions with non-homologous antisera, it is desirable to 

 dilute bloods as far as possible when testing them. This remark applies 

 more especially to medico-legal tests. Tests in which concentrated 

 sera are brought together and allowed to interact, as in the experiments 

 of Friedenthal and others^, are liable to lead to false conclusions, 

 especially when reactions with non-homologous bloods are to be excluded I 

 This is also true of tests carried out with strong solutions. 



Linossier and Lemoine (25, i. '02), working with anti-human serum, 

 having, they state, great power, found it necessary to add it in the 

 proportion of 25 : 1 of human blood in dilution, to remove all the 

 precipitin; in other words, 25 volumes of antiserum were neutralized by 

 one of blood. The proportion of antiserum added to a given blood for 

 this purpose will naturally vary according to its strength. As is stated 

 on p. 89, an excess of blood leads to precipitum solution. This has also 

 been observed by L. Camus, and Linossier and Lemoine (21, in. '02), 

 who dwell upon the importance of not using an excess of serum in 

 solutions to which antiserum is added. Eisenberg (v. '02, p. 293) finds 

 that dilution per se affects the interaction of equivalent proportions 

 of precipitin and precipitable substance. Whereas equivalent propor- 

 tions lead to precipitation in small quantities of fluid, he states that no 



' See also under Antiprecipitins, p. 149, and Normal Precipitins, p. 150. 

 - See p. 73, Linossier. 



