INFECTION AND RESISTANCE 



Experiments on Cocto-precipitin. Table II (March 23, 1913). 



Cross titrations dilutions of sera in salt solution boiled 5 minutes, 

 precipitated with antisera produced by injections with similarly boiled material. 



The readings here indicated were taken by "ring" test at the end of 30 

 minutes. 



* These controls were necessitated by the fact that the boiled serum suspensions were them- 

 selves turbid and occasionally showed slight settling on standing. 



be done, as advised by Schmidt, by the "70 precipitins," or with 

 native precipitin as practiced by Fornet and Miiller. 



The specificity which is the basis of the practical value of the reac- 

 tions that we have discussed is spoken of as "species" specificity 

 since it has been found that the blood serum of rabbits or other ani- 

 mals into which the serum of another animal has been injected 

 reacts, not only with the homologous blood serum, but also with 

 extracts of the various organs of the particular species of animal 

 which furnished the serum. Thus if we immunize rabbit, let us say, 

 with sheep serum the resulting precipitin will react, not only with 

 sheep serum, but also with extracts of sheep spleen, sheep liver, etc. 

 It seems that every species of animal possesses throughout its tis- 

 sues a particular variety of protein, fundamental to its general 

 metabolism and peculiar to its species. On the other hand, we have 

 seen in the preceding discussions how chemically slight the changes 

 in a protein may be which can alter materially its antigenic nature, 

 and it is a logical deduction that different organs of the same animal 

 might contain antigenic constituents qualitatively different from the 

 general serum protein. There are undoubtedly in many organs 

 protein complexes which are peculiar to them and not present in 

 other organs, and it would be reasonable to expect therefore that 

 immunization with separate organ substances would lead to the pro- 

 duction of sera of specific precipitating power for the protein of that 

 particular kind of organ. This is not ordinarily obtainable, how- 



