69 



virulent blood, (semm or peritoneal liquid) taken from sick animals. 

 The liorse-sickness anti-serum obtained from liyperimmunised animals 

 proved to have effective anti-bodies against horse-sickness virus, but 

 accidentally also isoly sines which became active in some injected 

 animals, and killed tliem by haemolysis. 



Hence it was necessary 



(1) to recognise a haemolytic serum amongst the immune sera 



by experiments in a test tube ; 



(2) to find out the haemolytic limit below which a slightly 

 haemolytic serum could be used without any danger for 

 injection. For this purpose it was advisable to express the 

 haemolytic power by figures which he called the haemolytic 

 index ; 



(o) to find a method of hyiDerinimunisation which gives only 

 horse-sickness anti-bodies and no isolysines, or as little as 

 possible. 



Tlie exiDcriments were cariied out with the object of solving these 

 problems in a practical luanner. Dr. Theiler kiiadly permitted me to 

 use his exx^erimental records. I am here publishing a collection of 

 them arranged from the theoretical standpoint* of haemolysis, which 

 is somewhat different from the abovementioned guiding ideas. It so 

 haijpened that several experiments which, from my i^oint of view, 

 would have been useful in completing a series of deductions, were not 

 carried out. 



Methodology. 



In a series of tubes, containing each 2 c.c. of the sterile serum 

 which had to l)e tested, were added 0-5 c.c. of defibrinated sterile 

 blood of different animals, horses, or mules. The mixtures were kept 

 at 37° for two hours, then placed in an ice chest over night. The 

 change which took j)lace was recorded as follows : — 



Marks. 



1. Trace — indicates a slight red discolouration of the lowest layer 



of the serum just above the deposit. 



2. Slight — indicates the haemaglobin diffused up to the top of 



the liquid. 



3. Distinct — indicates a deep red discoloiiration of the entire 



serum, but tlie deposit still dark. 



4. Complete — indicates the deposit colourless, and the haema- 



globin completely diffused out of the corpuscles. 



The Haemolytic Index. " *" 



Example : 10 tubes, containing all the same serum, but blood from 

 10 diflferent horses. 



(a) Number of tubes showing haemolysis = 5 (i.e. the blood of 

 5 horses is dissolved by this serum). 



* CompEire : W. Frei, Zur Theorie der Haemolyse, etc. Zeitsohrift fur Infektionskrankheiten, 

 parasite Krankbeiten, Hygiene der Haustiere, 2, 158 and 3G0, 1907. 



