Contagious (^Zymotic) Diseases. 9 



-red cells of man, pigeon and rabbit, red cells of man were added 

 and the whole centrifuged. The clear liquid left will no longer 

 ■clump the red cells of man, but will still clump those of the pi- 

 geon and rabbit. The agglutinins in the blood of one animal are 

 thus shown to be many, one acting on a given microbe or on the 

 red globules of one animal and another on those of another. 



The power of the agglutinins survives a temperature of 60° C. 

 but is lost at 65" C. Thus by heating a serum to 55'' C. the 

 haemolytic action is destroyed while the action of the agglutinins 

 is retained . 



Precipitins. If a rabbit is injected with the serum of horse, 

 •chicken or eel, and the serum of this rabbit is later mixed with 

 the serum of a horse, chicken or eel, as the case may be, the 

 latter becomes cloudy by reason of the precipitation of a portion 

 of the albumen. The substances in the rabbit's serum which de- 

 termine the precipitation of a portion of the albumins are known 

 as precipitins. I^eblanc finds that in the majority of cases the 

 precipitate is made up in part of albumin from the serum operated 

 on, but mainly of pseudo-globulin from the specific serum. The 

 specific serum may operate equally on the serum of two nearly 

 related animals'. Thus the serum taken from the rabbit which 

 liad been first injected with chicken serum, precipitates the 

 normal serum of both chicken and pigeon. These two animals 

 are supposed to have common receptors. 



Without going further in the elucidation of precipitins and 

 their relations, it may be said that in them as in the agglutinins 

 we have to a certain extent a parallelism with the production 

 of antitoxins by the introduction into the living body of the 

 toxins of a given disease. No method for the utilization of the 

 precipitins for protective purposes has been successfully worked 

 out, yet they have been availed of to differentiate the flesh of 

 one animal from that of another for which it has been sub- 

 stituted : — the flesh of the horse from that of the ox, or that of 

 the dog from that of the sheep. 



Antibodies. These are protective agents produced by the animal 

 cells, when they are submitted to successive^ encreasing doses of 

 the inimical material of microbian or other origin. Thus treat- ' 

 ment with hemolysins develops antihmmolysins, isolysins develop 

 anti-isolysins, agglutinins develop anti- agglutinins, precipitins 



