THE PHENOMENON OF PRECIPITATION 255 



In another series he finds: 



ANTIHUMAN PRECIPITATING SERUM 



Tested against Precipitate 



Man 100% 



Chimpanzee (loose precip.) 130% 



Gorilla 64% 



Ourang 42% 



Cynocephalus mormon 42% 



Cynocephalus sphinx 29% 



Ateles 29% 



Among the primates the highest figures with antihuman serum are 

 given by the chimpanzee. Other bloods than those of the primates 

 gave slight reactions or none whatever with the antihuman serum. 



In addition to these results the relationships within the dog 

 family, the horse family, and many other kinships similar to these 

 were confirmed. In every case the precipitin reaction was con- 

 sistent with the results of other methods of classification, and ^N"ut- 

 tall's work is an extremely valuable aid to zoologists in disputed 

 questions of animal relationships. 



These facts are the more surprising in that they demonstrate 

 species differences between the proteins of various animals which 

 are not determinable by known chemical methods. How funda- 

 mental these differences are and how delicate the reaction, is further 

 shown by experiments of Uhlenhuth, in which he obtained a specific 

 antihare serum by treating rabbits' with hares' blood, an astonishing 

 result in view of the close zoological relations between these animals. 



Isoprecipitins, that is, precipitins resulting from the treatment 

 of animals with blood of another individual of the same species, have 

 also been described by Schiitze and others. They are not, however, 

 regular in their appearance, nor are they very potent when obtained. 



Since the reaction is equally applicable to vegetable proteins, 

 similar investigations on the interrelationship of different varieties 

 of wheat have been carried out by Magnus. 28 



The methods of performing precipitin tests for forensic or other 

 purposes is extremely simple. Nevertheless, there are a number of 

 theoretical considerations which we must take up in order to make 

 clear the limitations of accuracy and conditions of control which are 

 involved in these reactions. From our discussion of the nature of 

 precipitinogen it follows that blood stains, etc., on linen or articles 

 of any kind will be suitable for precipitin tests even after they have 

 been exposed for considerable periods to unfavorable conditions, that 

 is, an environment in which they are subjected to exposure to light, 

 moderate heat, or drying. Thus blood spots, etc., if kept dry and in 

 28 Magnus. Cited from Uhlenhuth, loc. cit. 



