Till-: PRECIPITIN REACTION. 



95 



The animals whose sera are shown are usually considered to 

 be related to each other as follows: pig, beef, sheep and goat 

 belong to the order Artiodactyla ; horse belongs to the closely 

 related order Perissodactyla ; dog, human and guinea pig belong 

 to the distantly related orders, the Carnivora, Primates and 

 Rodentia respectively. Except for the horse the reactions all 

 correspond to the accepted classification of these animals. 



Table IX. and Figs. 4 and 5 show the results obtained with 

 three antibeef sera. Two of these were obtained from rabbits, 

 the third from a fowl. A24 and C8 were injected with blood 

 serum from the same cow r . A22 was injected with serum from 

 two different cows. The homologous titers of these antisera 

 were not the same. In spite of this there is again a general 

 correspondence in results obtained with one important exception. 

 The latter is the rodent reaction. Whereas a very low value for 

 rodent blood was given by the rabbit antisera, a very much 

 higher value was obtained in the case of the chicken antiserum. 

 No one has ever been able to produce a rabbit antiserum which 

 would react against rabbit blood. There is therefore an inhi- 

 bition of precipitin formation in a rabbit when injected with 

 rabbit blood. This same inhibition w r ould be expected to extend 

 to animals closely related to rabbits, that is to other rodents at 

 least. No such inhibition for rodent blood would be expected in 

 chicken antisera and indeed as the data show a much greater 

 reaction is then obtained. It seems therefore that chicken anti- 



TABLE X. 



REACTIONS OF ANTISHEEP SERA. 



