In the preceding paper ( 1), there was presented a summary of the maximum titers of cold agglutinins found in 1069 cases of a variety of conditions, including the various infections of the respiratory tract that are commonly encountered in this vicinity. Significant titers (in dilutions greater than 20) were Methods. The method used in the tests for cold agglutins was given in detail in the preceding paper (1). For the present study, the specimens of venous blood were all collected under sterile precautions and the serum was separated from the clotted blood, either at room tempera-1 Hereafter referred to for brevity as "atypical pneumonia." ture or, more often, after the blood had been kept at 370 C. for a short while. The cleared sera were stored in rubber stoppered tubes at 5 to 100 C. Specimens, averaging 3 per patient, were obtained at suitable intervals. The tests were carried out either on the day when the blood was obtained or within a few days. Equal volumes of serum and 2 per cent saline suspensions of 2-to 4-day-old red blood cells from individual group 0 donors were used. The titers are recorded as the reciprocals of the highest final dilutions of serum giving 1 + agglutination at 0 to 50 C. and complete dispersion at 370 C. RESULTSThe conditions under which the present cases were studied unfortunately did not permit frequent observations throughout the entire course of the acute illness and prolonged observations during convalescence in every instance. Data concerning certain of the features to be considered are, therefore, based on limited numbers of cases. In the analysis which follows, the time relationships are referred to the day of onset of symptoms. In most of the cases, this could be ascertained quite accurately, but, in a few instances, it was only approximated. Time of appearance, decline, and disappearanceThe first postitive tests ( Figure 1A) were observed between the seventh and twenty-seventh days, but mostly during the second or third week. The last negative tests in the same cases were obtained before the end of the second week in all but 2 of them. The maximum titers (Figure 2) occurred mostly between the eleventh and twentyfourth days. There were a number of cases, however, in which the maximum titers were not attained until the fifth week or later, and in 4 cases, maximum titers of 40 to 160 were observed between the fourth and eighth days and lower titers obtained later. There was no definite correlation between the maximum titers and the time 458

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The isolation of an indifferent streptococcus (Number 344) from the lung of a fatal case of primary atypical pneumonia has recently been reported (1) and its biological properties described. Convalescent sera from more than onehalf of the cases of atypical pneumonia which were tested agglutinated this strain in final dilutions ranging from 1:10 to 1: 160 whereas agglutination in low titers occurred only rarely in the acute phase sera of such cases, in sera of normal individuals, or in acute or convalescent sera from persons with other respiratory diseases. The results of the streptococcal agglutination tests in atypical pneumonia correlated in many instances with the results of cold hemagglutination tests and with complement fixation tests with mouse lung antigen (2). In a number of cases, however, positive results were obtained with only one or two of these tests. Similar strains were also isolated from other cases.The authors did not feel that their evidence warranted the conclusion that the bacterium is a factor in the etiology of primary atypical pneumonia. Nevertheless, the fact that the positive findings were restricted largely to cases of atypical pneumonia is of some interest. The present paper deals with the results of serological tests in cases of atypical pneumonia and of other conditions using streptococcus 344 and another similar strain (E. S.) isolated in this laboratory. Tests for cold hemagglutinins were also done in all of the sera included in this study. MATERIALS AND METHODSA total of 255 sera from 78 cases of atypical pneumonia and 330 sera from 163 other individuals were used in this study. The latter include serial specimens from 6 cases of rheumatic fever and 82 individual sera from non-rheumatic carriers and non-carriers of hemolytic streptococci. All of the rheumatic patients and a number of the others had recent streptococcal infections. The antistreptolysin titers of these sera were known. The sera and the antistreptolysin data were generously provided by Drs. T.Duckett Jones and Benedict F. Massell, of the House of the Good Samaritan, who had carried out repeated throat cultures in these cases. Antistreptolysin determinations were also carried out in their laboratory on serial specimens from a number of the cases of atypical pneumonia. The sera in the atypical pneumonias were tested after they had been stored from 3 to 15 months. All but a few of the remaining sera were tested within a few weeks of the time they were obtained.Streptococcal agglutinations were carried out in essentially the manner described by Thomas et al. (1). A transplant of strain 344 was obtained from Dr. Thomas and strain E. S. was isolated in December 1943 from a sputum obtained late in the disease in a characteristic and severe case of atypical pneumonia. It was found in almost pure culture in this sputum and it had cultural, biological, and serological properties similar to those of strain 344. The antigens were prepared by washing the sediment of broth cultures 3 times in saline arid then resuspending it in s...

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