The Organhm and its Chemhirif 101 



and the antibody. The point of special significance for us 

 now is tliat the blood of a given species of animal has been 

 found to act as an antigen when injected into the circula- 

 tion of another species, and the extent of the reaction is in 

 large measure dependent on the degree of affinity between 

 the animal species to which the different bloods pertain. 



A particularly instructive case worked out by Hamburger 

 is given by Arrhenius. Serum from a rabbit was treated 

 with serum from a sheep, the rabbit serum being in this way 

 made to contain an antibody. The rabbit serum tlms af- 

 fected was then used for experimenting upon the serum of 

 a normal sheep, a goat and an ox, with a view to testing 

 (juantitatively the action in the three cases. The same 

 quantity of rabbit serum containing the antibody was used 

 in each case, as was also the same quantity of equally diluted 

 serum of the animals to be tested, and the amount of pre- 

 cipitate in each case was measured. The results given in 

 terms of the antibody or precipitin, rather than in that of 

 the precipitate are, in Arrhenius' words, as follows: "On 

 injection of sheep-serum into rabbit blood we have obtained 

 an antiserum containing per centimeter cube 300 equivalents 

 of ])recipitin against sheep-serum, 212 equivalents of preci- 

 pitin against goat-serum, and only 90 equivalents of pre- 

 cipitin against bullock-serum." ^^ This result is obviously 

 in agreement with the general zoological evidence that the 

 goat and the sheep are somewhat closer of kin than the 

 ox and the sheep or the ox and the goat. 



Another inference of quite different import drawn from 

 the experiments is not to be missed, namely, that the dif- 

 ferent amounts of precipitation in the three sera is not due 

 merely to a quantitative difference in the precipitin con- 

 tained in the rabbit serum, but that there are really three 

 precipitins involved. This conclusion, Arrhenius points out, 

 se^ms necessitated by the fact that a unit quantity (1 c. c.) 

 of the normal serum from each of the three animals tested 



