232 SPECIFICITY 



serum precipitins is rarer, but occurs, according to Noguchi, in 

 cold-blooded animals (crustacea, etc.), and Lamb found in normal 

 rabbit serum a precipitin for cobra venom, and Obermayer and 

 Pick one for dysglobulin of egg-white in the same fluid. 

 N^The relation of the precipitins as regards specificity forms a 

 difficult and most important question. It was at first thought 

 that the specificity was a sharp one, and that a serum prepared by 

 the injection of human serum would only precipitate with human 

 serum, and a lacto-serum prepared by the injection of cow's milk 

 would only precipitate with that fluid, and not with the milk of 

 other animals. Thus, Uhlenhuth prepared a precipitin by inject- 

 ing a rabbit with ox serum, and found it gave a precipitate with 

 that fluid, but not with the serum of the horse, donkey, pig, sheep, 

 dog, cat, deer, fallow-deer, hare, guinea-pig, rat, mouse, rabbit, 

 chicken, goose, turkey, or pigeon ; but he also showed that anti- 

 egg serum was not sharply specific, and would coagulate solutions 

 of albumin from eggs other than those of the species used for the 

 injection. Wassermann and Stern also showed that antihuman 

 serum would react, though but slightly, with the serum of the 

 baboon, and Stern confirmed this, and found it reacted with the 

 serum of other monkeys. Hence the idea gradually arose that 

 the precipitin obtained by the injection of a serum from one species 

 of animal is not specific for that species, but will give a precipi- 

 tate, though of less amount, with the sera of other species, provided 

 that they are sufficiently closely allied zoologically. This has been 

 especially studied by Nuttall, who expresses this relationship 

 between species close together in the animal scale as a " blood- 

 relationship." He showed that, provided the serum were powerful 

 enough, it would react with all the bloods of animals in the same 

 great division of the animal kingdom (mammalia, birds, reptiles, 

 amphibia, etc.). Thus, a strong antihuman serum will give a 

 precipitate with human serum, even when highly diluted, with 

 apes, monkeys, etc., but not in such high dilutions, and a slight 

 trace of precipitate after a long period when mixed with the sera 

 of more remote mammalia, but no precipitate with the blood of 

 birds, fishes, etc. Quite similar relationships hold with the 

 lacto-sera and with the precipitating sera for muscle proteids; 

 the anti-sera for egg proteids is apparently less specific. 



Hence we deduce that the precipitins are not specific as regards 

 the animal species from which they are derived, but possess that 

 partial specificity seen in the cytotoxins and in the " group 



