The virus of poliomyelitis contained within the spinal cord and medulla of human beings and monkeys withstands glycerolation for many years. The specimens tested had been kept for 4 and 6 years respectively in 50 per cent glycerol at refrigerator temperature.
The symptoms and lesions caused by this virus are identical with those produced by that contained in the more recently collected spinal cord and medulla.
The specimens had lost a part of their activity under the conditions described, necessitating larger and repeated doses to induce infection. Whether this difference is due merely to quantitative reduction in number of viable microorganisms or to qualitative alterations under the influence of the mildly antiseptic glycerol has not been determined. An ineffective inoculation of tissues containing the virus does not increase resistance, but rather diminishes it, so that a subsequent injection, inadequate in itself, may cause experimental poliomyelitis. This power of survival under adverse conditions may not be without significance in respect to the recrudescence of poliomyelitis in a given locality and after a lapse of years. Hitherto this phenomenon has been accounted for by assuming a fresh importation of a virus of pronounced pathogenic power. It is possible that the explanation in some instances resides in the renewed activity of specimens of the virus surviving from a previous epidemic, while in other instances a fresh introduction actually takes place from a remote focus of infection.
The infectious nervous tissues employed in these experiments did not yield in culture streptococci or other ordinary bacteria.