From the foregoing experiments it appears that with the filtered nasopharyngeal secretions from early cases of typical infections common colds in the first 3 to 18 hours of the disease, a similar condition can be transmitted to man. With the unheated but not with the heated secretions from four of six such patients we have succeeded in transmitting an affection indistinguishable from common cold to four men and in two instances the condition was conveyed from the person with the experimental disease to a second individual β€”in all, therefore, to six supposedly normal subjects. The periods of incubation in the experimental disease varied from 8 to 48 hours. We failed to obtain these results with the filtered secretions from cases of common colds 18 and 20 hours after the onset of symptoms and from a patient with the experimental disease 20 hours after the first symptoms. It would appear that the secretions are more active in the early hours of the affection. We also failed in the two instances in which colds were caused by exposure to the elements, or chilling of the body, and not by definite contact with other cases of common colds.

Intratracheal inoculations in rabbits with unfiltered and filtered nasopharyngeal washings obtained from patients with common colds induce no characteristic or distinctive effects on the tissues, from which no constant, pathogenic agent has, as yet, been recovered. In comparison, similar material from cases of epidemic influenza do, however, cause particular changes in the blood and lungs of these animals, cultures of the lungs often yielding Bacterium pneumosintes. In view of these facts and since the clinical pictures exhibited by these diseases differ, the conclusion may be drawn that infectious common colds and epidemic influenza are separate and distinct diseases. On the other hand, the negative results obtained with materials derived from common colds and from parallel series of experiments with secretions from supposedly healthy persons, serve as a control to the effects produced with the nasopharyngeal washings obtained from influenza patients.

Aerobic and anaerobic cultures of the filtered nasopharyngeal washings from 40 early cases of infectious common colds have thus far yielded no constant, pathogenic agent which can be regarded as the incitant of the disease. The filtered washings of nineteen cases were studied by the combined method of Smith-Noguchi fluid medium and anaerobic blood agar plates. In these instances representatives of the three groups of anaerobic filter-passing, Gram-negative bacteria, described by Olitsky and Gates were cultured from twelve patients. The irregularity of their occurrence not only in common colds but in influenza and supposedly normal persons and their lack of pathogenicity for rabbits and man indicate that these bacteria are not peculiar to common colds. This method has opened to view a number of hitherto undescribed microorganisms which can be found in different respiratory affections and in health. Furthermore, by morphological, cultural, and serological means, the separation into distinct species of each of these groups of bacteria has again been demonstrated. It is noteworthy that Bacterium pneumosintes was not found in any of the cultures from the 40 patients.

Special attention was given to the detection of elements similar to Foster's globoid bodies in the cultures derived from common colds and from the experimental disease in man, and from the lungs of inoculated rabbits. We have not been able to determine the presence of these bodies, although the precipitate which forms in fresh rabbit kidney tissue-ascitic fluid medium was illusory in such relation since it was a common experience to find this precipitate simulating the globoid bodies of poliomyelitis. Still more disturbing is the fact, that these particles could be carried over from subplant to subplant and even showed pseudo colony formation in the Noguchi semisolid medium in tubes. But when the particles were put to rigorous test for a living and multiplying organism, the tests failed to reveal multiplication.

The increasing importance of the tissue-ascitic fluid medium in bacteriological technique warrants a detailed description of the requirements necessary for the determination of the living nature of formed elements in cultures in this medium, (a) No one method of staining can be relied upon, for stain precipitate in itself adds to the confusion. A specimen for examination should be stained separately by Gram's and Giemsa's methods and with another nudear dye, such as polychrome methylene blue. As a rule, microorganisms will reveal their morphological characters in more than one stain, whereas precipitate may be found in only one and not in the others. The experienced eye will discern the precipitated particles in selected parts of the stained preparation where they often occur in enormous numbers, clumped into irregular masses of varying forms from the periphery of which there is a gradual fading out to finer, more uniform structures. (b) In addition, suspected growths should be tested in the dialysate medium of Gates since by this method the precipitated material of the medium is kept from admixing with the growth, and a clear view of any microorganisms, if present, is obtained, (c) Another requirement is colony formation of the suspected culture. This is an absolute essential and can be effected by planting the material to be tested on solid plate media, incubated aerobically, and anaerobically in Brown's jar. Semisolid medium in long tubes should also be employed but care is needed to avoid mistaking small particles of precipitate for actual colonies of bacteria. To make certain of growth of microorganisms in semisolid medium, however, subplanting to a precipitate-free, dialysate medium is required.

By following this method minute microorganisms which are obscured, or simulated, by precipitate in the Smith-Noguchi medium, can be identified.

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