314 Quantitative Precipitin Tests 



" The fluctuations above and below the means in the human series 

 are '0012 c.c. or 4%, and in the ox series '0029 c.c. and '0018 c.c. 

 respectively, or 12/o and 7/o- 



" In order to arrive at the most trustworthy figures possible, in most 

 experiments two observations were made under identical conditions in 

 the hope that by this means the experimental error might be reduced 

 to a minimum. 



" In measurements of this kind with every precaution probably a 

 margin of 10/o must be allowed for experimental error. 



"Throughout these experiments the aim has been to indicate by 

 measurements the effects of varying conditions on the formation of the 

 precipitum as compared with controls. It must be stated, however, 

 that with every precaution the measurements of the same set of 

 materials on different days are not identical, although the proportions 

 which the various members of the set bear to each other remain fairly 

 constant. Hence though improvements in the technique of measurement 

 may result in more accurate and constant figures, yet it is improbable 

 that the general results will be materially altered." 



Measurements could be made with reasonable accuracy down to 

 '001 c.c. but of course it would be a mistake to attach importance to 

 minute reactions of 10 % and under, unless results of repeated tests are 

 concordant. 



The results in spite of all these possible sources of fallacy certainly 

 speak for themselves, and show beyond question that much may be 

 accomplished by the use of the precipitin tests in the study of animal 

 relationships. We believe that we have but entered on the threshold 

 of a method of investigations which is bound with time to yield useful 

 data. This investigation must necessarily be regarded as preliminary 

 in character. A careful selection of material to work upon, especially 

 material which is readily obtained, together with care directed to 

 excluding the sources of error above mentioned, are indicated in the 

 future. 



In view of the extent of the work, Dr Graham-Smith, whose paper 

 follows, was entrusted with similar investigations upon the bloods of 

 lower animals than those here considered (see p. 336). 



The tests here recorded were made upon the bloods of Primates, In- 

 sectivora, Carnivora, Ungulata, Cetacea, Marsupialia, and Aves by means 

 of the following antisera. The method of obtaining antisera has already 

 been described elsewhere by Nuttall (p. 51). 



