116 



The Nature of Precipitin Reactions 



the anti-sheep serum slight opalescence was noticed at 66 C., which 

 became more pronounced at 68 C. The following table shows that a 

 marked reduction in the precipitum-forming power coincided with the 

 visible change. 



When the slightly opalescent antiseriim was added to a serum 

 dilution a slight cloudiness appeared throughout the fluid. The more 

 markedly opalescent serum differentiated itself as it settled to the 

 bottom of the tube as a very definite cloud. After shaking the tube 

 the fluid appeared cloudy throughout, but remained in this condition, no 

 precipitum settling to the bottom. 



The precipitum settled most quickly in the unheated specimens, and 

 the rate of formation of precipitum decreased as the temperature, to 

 which the antiserum had been exposed, increased. 



Up to 60 C. no change in the precipitum-forming power was found 

 in either the anti-ox or anti-sheep sera, and both gave no trace of 

 precipitum when heated beyond 67 C. Between 60 C. and 67 C. the 

 quantity produced in each case was diminished. The figures given are 

 the mean of two estimations in each case." 



Anti-ox (heated for 5 minutes) 



Anti-sheep (heated for 1-5 minutes) 

 Precipitum Percentage Remarks 



0075 100 



