Pure LS-antigen of vaccinia contains 15.8 per cent N and 50.6 per cent C. These analytical data together with the absence of lipids, phosphorus, nucleic acid, and glucosamine in preparations of the antigen confirm the protein nature of the substance. The action of proteolytic enzymes on LS offers further confirmation of the protein character of the antigen.

Both the L- and S-activities of the antigen are destroyed by digestion with papain. The effects of crystalline chymotrypsin on LS-antigen are particularly interesting for, under proper conditions, this enzyme destroys the serological activity of the S-portion of the molecule without affecting the L-portion. This newly prepared degradation product of LS, called LS'', contains the same amount of N as the native substance but unlike LS, it forms needle-shaped crystalloids.

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