PRECIP1TINS 109 



cipitates, or only cloudings. A less highly active 

 serum will likewise cause a marked precipitate in 

 the homologous blood solution, and a slight pre- 

 cipitate, or only a clouding, at the most, in a closely 

 related species. For example, the serum of a rabbit 

 which has been treated with sheep blood produces 

 a marked precipitate in a solution of sheep blood ; a 

 slight precipitate in a goat -blood solution ; and a still 

 fainter one in an ox-blood solution. In some in- 

 stances the two latter will show only a clouding. If 

 we employ a very weak serum, even the cloudings 

 will be absent, and a precipitate is formed only in 

 the sheep-blood solution. If human blood or 

 blood serum has been injected, the clouding and 

 precipitation will occur most readily (aside, of 

 course, from human-blood solution) in that of apes. 

 In the precipitin reaction, therefore, the relationship 

 of the single animal species is an important factor. 

 This peculiar behavior has first been thoroughly 

 studied by Nuttall l who made observations on 

 five hundred different animals. As a result of these 

 we know that a weak human-blood antiserum, 

 besides reacting on human blood, causes a clouding 

 only in the blood of anthropoid apes (chimpanzee, 

 gorilla, orang-outang) ; a stronger serum causes a 

 clouding also in the blood of other monkeys ; finally 



1 British Medical Journal, 1901, Vol. ii, and 1902, Vol. i. 

 See also Nuttall, Blood Immunity and Blood Relationship, 

 1904. The Macmillan Co., N. Y. 



