Seasonal Variation in Susceptibility of Animals to Tetanus Toxin

Abstract

During the course of certain investigative work with tetanus toxin,∗ it was noted that there appeared to be a consistent variation in the susceptibility of animals to the same lot of toxin. Judging from the time of onset and the severity of the symptoms in acute and subacute poisoning in the rabbit and guinea pig, there was found an increased susceptibility during the summer months and decreased susceptibility during the winter months. Since this observation was rather incidental, it was decided to determine the actual minimal lethal dose of the toxin at various periods during the year.

For these toxicity studies, guinea pigs were used in all experiments. The toxin was kept in an icebox in small vials sealed in carbon dioxide. Approximately 100 guinea pigs were used. The work was carried on over a 2 year period.

The minimal lethal dose as determined during October and February and a year later in November was found to be from 0.004 to 0.005 mg. per kilo of body weight. This amount will kill approximately 8 out of 10 animals. All animals die with 0.006 mg. per kilo. The minimal lethal dose during the months of June a year apart was from 0.002 to 0.003 mg. per kilo. This amount again killed approximately 8 out of 10 animals and all died with 0.004 mg. per kilo.

If the toxin be thought to change spontaneously on long standing, it of necessity should become either less or more potent. Since identical figures were obtained during the same seasons a year apart, i. e., greater toxicity both summers and lesser toxicity both winters, we are forced to conclude that the differences observed reside in the conditional state of the animals and not to changes in the toxin.