SPECIAL PROPERTIES OF BLOOD SERUM. 26/ 



larly vulnerable or susceptible organs. The soluble serum con- 

 stituent which is normally present in small amount or which 

 may be developed there to neutralize the toxin in some man- 

 ner is called an antitoxin in the restricted sense. There is 

 reason to believe that the two things combine with each other 

 in a true chemical union and leave a soluble inert product. 



Precipitins. The serum of normal blood contains constit- 

 uents antagonistic not only to toxic substances but to other 

 sera as well. The serum of one animal tends to precipitate 

 or render cloudy the serum of another. This effect may be 

 greatly increased by a kind of cultivation, which may be illus- 

 trated in this way. Rabbits' blood has normally some antag- 

 onism for ox blood, but if sterile ox serum be injected into the 

 rabbit, intraperitoneally or intravenously, beginning with 

 small doses and increasing through a number of days, a con- 

 dition is finally reached in which the rabbit blood serum shows 

 a very strong precipitating power for ox serum. The small 

 amount of anti body in the rabbit's blood has evidently in- 

 creased enormously through this treatment. The organism 

 through the attack of the foreign serum gradually develops a 

 protective agent which acts through exclusion or precipitation. 

 This serum constituent is called a precipitin. 



A vast number of experiments have been made in this field 

 and the subject has importance in different directions. We 

 recognize not only the normal effort of the blood to protect 

 itself in this way, but also the remarkable power of develop- 

 ment in the peculiar anti body here concerned. From another 

 standpoint, however, the phenomenon has assumed even 

 greater importance and that is in the identification of blood. 

 This precipitin reaction like the others is specific and the serum 

 of the rabbit immunized with ox serum will react only with 

 the ox serum. But precipitins do not seem to be formed in the 

 blood of animals which are closely related. The serum of a 

 rabbit which has been treated with pigeon serum will not react 

 with chicken serum; an anti rabbit serum cannot be secured 

 by treating a guinea-pig with the serum of rabbit's blood. 

 These general facts have been confirmed by many observations. 



