The Occurrence during Acute Infections of a Protein Not Normally Present in the Blood

The serum obtained from human beings and monkeys during the acute phase of diverse infections contains a protein which is precipitable by the C polysaccharide of pneumococcus. The distribution of this protein in acute phase serum has been studied, and the effect of calcium on the precipitation reaction with the C polysaccharide is described. Other distinctive features of this reaction are discussed. 1. When heated above 65 degrees C., serum obtained from patients during certain acute infections loses the property of reacting in precipitation tests with the C polysaccharide of pneumococcus. The loss of activity under these conditions occurs at temperatures known to denature many proteins. 2. The reactive component in "acute phase" serum which precipitates with the C polysaccharide is tentatively regarded as a protein. 3. The reactive substance is associated with the albumin fraction of serum. 4. In the reaction between patients' serum and C polysaccharide, flocculation is conditioned by the presence of calcium ions. 5. The following distinctive features of the C-reaction are discussed with reference to known characteristics of antigen-antibody phenomena: (a) the occurrence of the reactive component in blood only during the acute stage of the infection; (b) the lack of specificity of the reaction with respect to the inciting cause of the disease; (c) the presence of the active substance in the albumin fraction of the serum; (d) the action of calcium in producing flocculation.