Further Observations on the Poliocidal Property of Pregnant Mare Serum. ∗

We have previously been interested in the changes that occur with pregnancy in man and animals with reference to the ability of the serum and of other biological substances to neutralize the virus of poliomyelitis in vitro. 1 , 2 In an earlier paper 2 it was reported that the serum of 2 pregnant mares when combined in high dilutions with this virus was capable of bringing about its inactivation. No data were available at that time to indicate whether the normal serum of the same non-pregnant animal possessed similar properties. Again, since our work included tests on 2 animals only, it was unknown how regularly the same phenomenon could be elicited with the serum of other pregnant mares. The most important gap in the observed facts, perhaps, was the absence of information as to whether or not the poliocidal power ran parallel with the content of the serum of gonadotropic hormone. It is the purpose of this communication to supply the experimental facts which will answer the questions raised above.

Serum obtained from 5 mares at various stages of pregnancy and, in most cases, after foaling also, were available through the courtesy of Dr. Fred F. McKenzie of the Agricultural College of the University of Missouri, Columbia, Mo. We should like to express our sincere gratitude to Dr. McKenzie for supplying US with this material, for without his untiring cooperation these studies would have been impossible. The samples represented unpreserved, fresh bleedings which were shipped by express. Immediately upon arrival at this laboratory they were tested for virucidal property and for hormone content. The technique of the virucidal test followed the same general principles previously employed in work of this kind, i. e., 0.8 cc. of serum or serum dilution were combined with 0.2 cc. of a 10% virus suspension; the mixtures were incubated for 1% hours at 37°C., kept in the icebox over night, and the following morning injected intracerebrally into individual monkeys.