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more potent than the parent in the Clauberg test, was less potent as an estrone antagonist; thus the ratio was grossly reduced. Incorporation of a double bond at the 9-10 position of 1 7~-chloroethynyl-13p-ethyl-1 7-hydroxygon-4-en-3-one resulted in decreases of both activities; however, since the decrease in progestational effect was greater, the ratio was considerably increased. 1 7~-Chloroethynyl-13fl-ethyl-l7-hydroxygon-4,9-dien-3-one was less potent in the Clauberg test, but more potent in the anti-estrogenic assay than the lower homologue. Thus the ratio of potencies was decreased.13~-Ethyl-17-hydroxy-l7~~-methylgon-4-en-3-one was more anti-estrogenic and less progestational than its lower homologue. 1 7~-E thy1 -1 7-hydroxy-13p -me thylgon-4 -en-3 -one (norethandrolone) was less potent in both assays than its 18-homologue (norbolethone) , which because of a greater anti-estrogenic potency had a higher ratio. Incorporation of a double bond in the B-ring of norbolethone to form 13p, 1 7a-diethyl-17-hydroxygon-4,9dien-3-one did not alter progestational potency, whereas the anti-estrogenic potency and the ratio were decreased, These data fail to indicate any direct correlation of progestational and anti-estrogenic effects. Although both these biological activities are often present in a single molecule, they do not appear to be necessary correlates.Summary. The progestational (Clauberg) and anti-estrogenic (mouse vaginal smear) potencies of various A4-3-oxosteroids are compared. The ratio anti-estrogenic potency,' progestational potency varies from 0.1 to 85, indicating that there is no necessary correlation between these parameters of steroid action.

Previous epidemiologic studies have shown that most primary atypical pneumonia illnesses in which cold agglutinins develop are associated with the agent first described by Eaton, Meiklejohn, and van Herick in 1944 (1-8). In addition the agent causes a spectrum of effects ranging from inapparent infection to febrile respiratory disease without pneumonia (5, 6).Recent studies have established that the organism, previously known as "primary atypical pneumonia virus" or "Eaton agent", is not a virus but a member of the genus Mycoplasma (pleuropneumonia-like organisms) (9-11). Thus, at least 30 strains have been grown in cell-free semisolid or liquid medium containing bovine heart infusion, yeast extract, and horse serum (10-13). Growth does not occur in the absence of serum or a suitable substitute such as egg yolk (10, 14). The colonies which grow on semisolid *agar medium exhibit a colonial morphology and fine structure characteristic of Mycoplasma (10). Certain microbial inhibitors such as thallium acetate, penicillin, and amphotericin B do not affect growth of the organism (10, 11). The agent is inhibited, however, by the tetracycline group of antibiotics (15).Until recently only four species of mycoplasma were known to infect man. These are M. hominis type 1, M. hominis type 2, M. salivarium, and M. fermentans. (16-18). When the atypical pneumonia organism was compared with these species by immunofluorescence or complement-fixation tests it was antigenically distinct (10, 19-21). It resembles M. fermentans in utilizing glucose and other sugars (22). The agent differs biologically from the four recognized human species of Mycoplasma by its ability to produce rapid and complete hemolysis of guinea-pig and horse red cells (23, 24). Under 662 R. M. CHANOCK

A characteristic of the parasitic pleuropneumonialike organisms (PPLO) is the requirement of serum or ascitic fluid for growth in vitro. Reference has been made by previous workers to some of the properties of the growth factor contained in serum. Tang, Wei, McWhirter, and Edgar (1935) reported that a hemoglobin solution had an enriching property for the bovine pleuropneumonia organisms. The apparent heat stability of this growth factor was alluded to by Nelson (1939). Tissue cultures employed for the cultivation of the fowl coryza bodies, considered to be PPLO, still supported their growth after being heated at 100 C for 1 hour or being stored in the refrigerator for 6 months. Chocolate agar, used for isolating the gonococcus, supported growth of PPLO according to Salaman (1946). Gilmore and Sprince (1949) reported that as little as 0.02 per cent bovine hemoglobin (Armour) permitted growth of PPLO in a liquid medium in the absence of serum. It was emphasized by Morton, Smith, and Leberman (1949) that native animal protein was unnecessary when these investigators observed symbiotic growth of PPLO with bacteria. Since the PPLO comprise a group of microorganisms with peculiar properties and the addition of serum or ascitic fluid to the medium is undesirable for many types of experiments, an attempt was made to isolate and characterize the growth factor present in serum and ascitic fluid. On the basis of work to be reported, it is thought that the essential growth factor for PPLO furnished by serum or ascitic fluid is a protein of low molecular weight, possibly of the globin type, or a degradation product of protein. EXPERIMENTAL METHODS AND RESULTS Eight strains of PPLO isolated from the male and female genitourinary tract served as the test organisms for all of the preparations tested for activity. These are the same eight strains used in previous work (

G-200 columns when either propionic acid or formic acid was used for elution. The phenograms obtained from column-separated polypeptide chains were compared, and no difference was found in either the L chain or H chain banding patterns of yG-globulin from bursectomized and normal chickens. These results indicate that the subunit of yG-globulin is the same for bursectomized and normal chickens.

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1. The presence of reversibly oxidizahle substances in melano. blasts that accelerate oxidatioii o f dopa by atmospheric aiid dissolved oxygen.

I This project has been supported by the Thos. H. Dougherty, Jr., Fund, and by grants from Smith, Kline and French Laboratories and the Department of Agriculture, Commonwealth of Pennsylvania.