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On the Weight of Precipitum obtainable in Precyntin Interactions 
with Small Weights of Homologous Protein. 
By Professor D. A. WELSH and Dr. H. G. CHAPMAN. 
feted by Dr. C. J. Martin, F.R.S. Received December 17, 1907,—Read 
February 6, 1908.) 
(From the Physiological and Pathological Laboratories of the University of Sydney.) 
In a previous communication* on precipitin reactions, we brought forward 
observations which led to the conclusion that the precipitum is derived 
mainly from the antiserum and not from the homologous protein. In a 
recent reviewt of our paper the suggestion was made that gravimetric 
evidence might be more conclusive. Acting on this suggestion, we have 
carried out experiments in which a considerable amount of antiserum was 
allowed to interact with a known small amount of homologous protein. As 
soon as the interaction was completed, the deposits were collected, washed, 
and weighed. In evety case the amount of dried precipitum exceeded the 
amount of dried homologous protein. The smallest precipitum obtained 
weighed more than twice, the largest more than 25 times, the homologous 
protein employed in the interaction. Former observationst had revealed that 
antisera require very different amounts of protein to ensure the formation of 
maximal deposits. -It was, therefore, to be expected that considerable 
variations would be obtained in the weight of deposits produced by small 
amounts of protein in different antisera. 
Method of Expervment. 
The antiserum was obtained from rabbits which were bled on the day of the 
experiment. One milligramme or 2°5 milligrammes dried egg-white or blood 
serum was dissolved in 10 c.c. salt solution and added to the homologous anti- 
serum, together with about 90 c.c. salt solution. The whole of the available clear 
antiserum, with the exception of less than 1 c.c. reserved for control obser- 
vations, was employed. The dried protein was prepared under aseptic 
conditions, and every precaution was taken to exclude micro-organisms§ — 
* Welsh and Chapinan, ‘ Roy. Soc. Proc.,’ B, vol. 78, p. 297, 1906. 
+ Mouton, ‘ Bulletin de l’Institut Pasteur,’ 1907. 
{ Welsh and Chapman, ‘Journ. of Hygiene,’ vol. 6, p. 263, 1906. 
§ We are unable to confirm Friedberger, ‘Centralb. f. Bakt., Orig.,’ vol. 43, 
pp. 490—494, March 5, 1907, in his statements regarding the prevention of bacterial 
growth by precipitin antisera, as our tubes tend to become infected in about 7 days. 
