JUGGLING WITH LIFE 



The blood of a rabbit that has attained this condi- 

 tion may then be used in testing for the presence of 

 the particular type of blood that was used in devel- 

 oping the anti-serum. For example, if human blood 

 was the kind injected into the system of the rabbit, 

 the rabbit's blood will now serve as a test for human 

 blood. 



MAN'S REMOTE RELATIVES 



It appears, however, that the anti-serum thus de- 

 veloped, while its most pronounced reactions will be 

 given with solutions of human blood, will also react 

 in a less marked degree with the blood of other 

 animals. 



If successive drops of the anti-serum are intro- 

 duced into one test-tube after another, as in the 

 Cambridge experiments, it will be observed that in 

 some tubes there is an immediate reaction, resulting 

 in a white precipitate. In other tubes the reaction 

 will set in only after some minutes; in yet others 

 after hours; and the remaining test-tubes will remain 

 permanently clear. It is these graded results that 

 enable the experimenter to test the blood relation- 

 ships of the different animals. 



It is found, for example, that when a test is made 

 with human anti-serum, an immediate reaction is 

 observed only in test-tubes containing human blood. 

 Less prompt and less marked reaction occurs in the 

 tubes containing the blood of the man-apes; still 

 milder reaction in the case of baboons, monkeys, and 

 marmosets in succession; and a long delayed or alto- 

 gether negative result in all other cases. It is ob- 



163 



