THE PRECIPITINS 235 



into an animal far removed in the zoological scale, and their 

 explanation is obvious in the light of what has been already said 

 with regard to individual differences in receptors. 



According to Ewing, an antihuman serum prepared from the 

 fowl shows a far higher degree of specificity than those obtained 

 by injections into rabbits. 



A short account of the practical application of the precipitins 

 may not be out of place. The chief is, of course, the medico-legal 

 identification of blood-stains, the chief exponents of which are 

 Uhlenhuth and Wassermann. The antiserum is obtained from 

 rabbits, which are treated by intravenous or intraperitoneal in- 

 jections at intervals of three or four days. The material used 

 for the injection may be blood obtained by venesection or vein 

 puncture, or from the placenta or from the cadaver, or pleuritic or 

 ascitic fluid may be used ; in any case strict asepsis is necessary. 

 The amount given rises from i to 3 or 4 c.c. in the case of 

 intravenous injections, or twice as much or even more in the 

 peritoneum. The course of treatment lasts three or four months. 

 Another and simpler method is to give larger doses up to 10 c.c., 

 or even more intraperitoneally at intervals of a week. The 

 animal is then chloroformed, and as much blood as possible 

 collected either from the heart or carotid artery. 



The fluid to be tested is prepared by maceration of the clot, 

 piece of stained linen, etc., with normal saline solution, or with 

 i per cent. NaOH. In the case of a very old stain, Ziemka 

 recommends the use of a strong solution of potassium cyanide, 

 which is subsequently neutralized with tartaric acid. This is 

 examined with the microscope and tested spectroscopically to 

 determine the presence of blood-corpuscles and pigments. The 

 solution is then filtered. Air is then allowed to bubble through 

 the fluid to make sure that proteid material has actually passed 

 into solution ; this is indicated by the production of a stable foam. 

 Three tests are made. In the first tube one part of the fluid under 

 examination is mixed with two of the antiserum, the second 

 contains the fluid alone, and the third antiserum plus normal 

 saline solution. Further controls, in which the antiserum is 

 mixed with diluted serum from animals other than man, may also 

 be made if necessary. The tubes are usually incubated and 

 examined from time to time, and a positive result is obtained if 

 there is a precipitate in the first tube and not in the others. 

 Further tests are then made with greater dilutions, and with a 



