AGGLUTININS AND PRECIPITINS in 



Biological Relationships. The question of the specificity of this 

 reaction has been somewhat confused by quotation from the famous 

 studies of Nuttall in regard to interrelationship of species. Nuttall's 

 book, published in 1904, was of the utmost importance to biology in 

 general, because it demonstrated anew by the use of the precipitin 

 reaction the interrelationship of animal species. He showed, for ex- 

 ample, the close biological relationships between man and the higher ape, 

 also similar relationships in the lower animals, as between the goat 

 and the sheep, the horse and the ass. Reference to the tables which 

 he published would seem to indicate, however, that the relationship 

 between man and the higher ape was so close as to be indistinguishable 

 by the precipitin reaction. An example in point is the statement which 

 . he makes that whereas human blood will respond to antihuman precipi- 

 tating serum to the extent of 100 per cent., the blood of the chimpanzee 

 responds to the extent of 130 per cent. These figures, however, refer 

 to the bulk of the precipitate thrown down in relation to standard 

 dilution of the various bloods employed. He used relatively low dilu- 

 tions, allowed the sera to remain in contact for several hours and then 

 measured the amount of precipitate. This, as can readily be seen, is 

 different from the method which is employed at the present time in 

 determining the titer of the sera against the immune serum. The 

 latter method is distinctly more delicate in determining the specificity 

 of the reaction. For that reason it is the method employed in the for- 

 ensic test of to-day, as well as in ordinary laboratory procedures. Fur- 

 thermore, we find at the present time that the test demonstrates its 

 specificity particularly in the presence of strong sera by reading very 

 shortly after the contact has been made. Hektoen offers an excellent 

 example of this in the following table (antihuman serum) : 



Blood 



Fish i-io 



Chicken i-io 



Rabbit o 



Guinea-pig i-io 



Rat i-io 



Cat i-io 



Dog i-io 



Swine i-io 



Sheep i-io 



Beef i-io 



Horse i-io 



Goat i-io 



Monkey (Macacus rhesus) i-ioo 



Human 1-5000 



It will be noticed by reference to the above table that the titer of 

 the serum used in this particular test was only 1-5000, and we would 

 expect an even greater difference between the titer with the different 

 animal sera if the antihuman serum had been of higher titer. Con- 

 cerning the group reactions in the precipitin test an interesting instance 

 is given by Hamburger in regard to the action of the serum of a 

 rabbit inoculated simultaneously with sheep serum, goat serum and ox 

 serum, all of which are fairly closely related to each other biologically. 



