Cats injected into the parotid gland and testicle with a bacterial sterile filtrate of the salivary secretion of children in the active stage of parotitis or mumps can be made to develop a pathological condition having several points of resemblance to the condition present in mumps in human beings.
After an incubation stage of from five to eight days definite changes have been noted in the temperature, blood leukocytes, and inoculated organs.
The temperature rise begins within twenty-four hours of the inoculations and reaches a maximum in from seven to fourteen days. The febrile rise fluctuates between 1° and 2.5° C.
The white blood cells begin to increase on the second day following the inoculation. The first change is a polymorphonuclear leukocytosis which precedes the glandular swellings. This initial rise is followed by a decline, after which the lymphocytes increase. The increase is confined to the small lymphocytes, which increase to from 7 to 10 per cent of their initial number.
The inoculated glands become swollen and tender. The swelling and tenderness become apparent from the fifth to the ninth days and persist for a variable period. The parotid changes are less constant or less obvious than are the testicular. The latter are constant and endure from eight to twelve days.
The rise of temperature and the leukocytosis precede the glandular swelling, but all the changes reach the maximum at about the same time, after which they decline gradually. What may be regarded as normal conditions are reestablished in four weeks or less.
The intraparotid and intratesticular injections of extracts of normal parotid gland and testicles may cause a mild rise of temperature and leukocytosis of brief duration, but swelling and tenderness are absent. The white cells increased are the polymorphonuclears and not the lymphocytes.
The intraparotid and intratesticular injections of filtrates of normal saliva may cause a mild rise of temperature of very brief duration, but leukocytosis, swelling, and tenderness do not appear.
The histological changes in the parotid gland when present consist chiefly of edema of the interlobular connective tissue with mononuclear interstitial infiltration about the ducts and elsewhere. In cases of long duration the ducts may be dilated. But in some instances the swollen gland while showing congestion and edema in gross showed inconspicuous changes under the microscope. The histological changes in the testicle are of two kinds: inconstant changes of cellular invasion between the tubules and swelling or even multiplication of the interstitial cells, constant ones consisting of degeneration of the epithelium and interference with spermatogenesis, a condition to which we have applied the term "spermatorrhexis."
The pathological conditions set up by the filtrate derived from the salivary secretion of cases of acute parotitis are intensified by successive transfers through a small series of cats of the extract and emulsion of the parotid gland and testicle previously inoculated.
The pathological changes are also prevented or reduced when the extract or emulsion is previously incubated with a quantity of blood serum obtained from a cat which has survived inoculation. Normal serum, on the other hand, has no such inhibiting effect.
The deduction from these experiments is to the effect that the salivary secretion in parotitis or mumps contains a filterable substance capable of setting up a series of definite pathological conditions when inoculated into the testicle and parotid glands of cats. Whether this active material is a microorganism and if so whether it is the specific microbic cause of parotitis or mumps remains to be ascertained.