882- TRANSACTIONS OF sfecTloN 1. 



10. Tlie Action of I' wo Sera on a Carcinoma occurring in Mice. 



By C. E. Walker. 



11. I'he Jiiological Method of Differentiating Blood-stains, 

 By Professor E. J. McWeeney, M.A., M.D. 



Tlie method referred to is that known as tbe Precipitin Test. It is a par- 

 ticular case of the general law that the animal organism reacts to the intro- 

 dnction of foreign substances of high molecular complexity by the production 

 of specific anti-bodies. The most satisfying explanation of this phenomenon 

 hitherto is the now well-known ' Side-Chain ' theory of Ehrlich. The foreign sub- 

 stance injected is known as the Anti-gen, and may consist of albumen, toxin, 

 or formed elements (blood-cells or the like). In the present case the anti-gen is 

 albumen derived from some animal and present in its serum, w-hile the anti- 

 body is called a precipitin, because, when brought in contact with specific 

 anti-gen, it manifests its antagonism by the production of an opalescence which 

 speedily thickens into a flocculent precipitate. As this only occurs (save in the 

 case of very closely allied species) with the specific anti-gen, the method affords 

 a reliaiile means of determining the species of animal from which a given speci- 

 men of serum or of blood-stain is derived. Originally applied by the late 

 Walter Myers about the year 1900 to the difl"erentiation of the various kinds 

 of egg- and serum-albumen, the reaction was used on an extensive scale by 

 Nuttall in his fundamental work on blood-relationship, and was applied first in- 

 Germany to the purposes of the medical jurist by Uhlenhuth, Wassermann, and 

 Schiitze. 



Since then the value of the precipitin test as a means of determining the 

 origin of blood-stains occurring on articles of clothing, surfaces, 'cc, in cases of 

 murder and other medico-legal inquiries has received State recognition in most 

 civilised countries. So far as the writer is aware, however, the method has not 

 been utilised by the Home Office in England, and this is his principal reason for 

 coming forward with the present paper. In Ireland when the advantages of the 

 method were first brought under the notice of the Crown authorities just six 

 years ago by the present writer they received immediate recognition, and the 

 writer has been employing the test for the past five years in medico-legal 

 practice with most satisfactory results. A few words as to technique. The 

 animals used for producing the precipitin are rabbits. As human anti-gen the 

 writer uses ascitic fluid or pleural etl'usion, aseptically collected Avhere possible, 

 otherwise stored over chloroform. The injections are intravenous, about 

 5 to 7 cc. being administered at intervals of four or live days. After eight to ten 

 such injections, the animal usually yields a satisfactory anti-serum, giving a dis- 

 tinct zone of opalescence when brought in contact with human serum diluted 

 to 1 in 500. After further treatment the reaction appears with dilutions of 

 1 per 1,000, and even 1 per 10,000. During the immunisation the power 

 of the serum is tested from time to time by withdrawing small quantities of 

 blood from the marginal vein of the ear by means of suitably curved pipettes. 

 The serum of domestic animals can of course be always readily procured for 

 injection, but suitable anti-gen for making anti-human serum is not always 

 obtainable save by those in hospital practice. In doing the test, as the quan- 

 tities of stain extract available are as a rule small, the observations are made in 

 very small test-tubes into which about 50 cmm. of the anti-serum is first 

 placed with a glass capillary, after which about 200 cmm. of the diluted serum 

 or stain-extract are allowed to run slowly down the side of the tube so as to 

 form a distinct line of demarcation. The liquids must be absolutely clear. The 

 writer makes his observations at room-temperature, and extends them over 

 a period of four hours. Controls are absolutely indispensable and must on no 

 account be omitted. Working on these lines the WTiter has obtained most 

 convincing results in every case. The chief sources of error are the so-called 



