L-forms of group A streptococci Size of viable particles and growth requirements
Filtrability is one of the characteristics of the L-phase of bacteria. The results of the filtration experiments reported in the literature indicate a diameter of the minimal reproductive unit of approximately 0.3t~. However, by measurements on photographs of slide cultures of the L-phase of several bacteria the diameter of the reproductive elements was found to be > 0.6/~ to 0.7t~ (Weibull and Lundin, 1962; Weibull, 1963). With the L-phase of two strains of group A streptococci the same discrepancy between the results of both techniques was obtained. Dependent on the expelimental conditions the filtration endpoint varied between 0.25/~ and 0.45u.. Slide cultures, observed by phasecontrast microscopy and photographed at regular intervals during incubation, showed that only elements having a diameter > 0.8~ developed into colonies. The possibility that the L-phase, due to its plasticity, is capable of passing through filters of smaller pore size than their diameter was investigated. Filtrates of 0.45~. filters were conceotrated by ultracentrifugation. Slide cultures inoculated with the sediment showed that the elements responsible for growth had a diameter ranging from 0.7tL-1.7tz. The results obtained indicate that the reproductive elements of the L-phase of the group A streptococci have a diameter > 0.8/~. Another property in which the L-phase differs from the parent strains is the need for special growth requirements (Sharp, 1954). However, results were obtained which indicate that these special conditions are not required during subculture. It proved to be possible to get luxuriant growth in a chemically defined medium of both the L-phase and the parent strains.
ISOLATION AND PROPAGATION OF MYCOPLASMA
We have used mainly media formulated according to the prescription of D. Herderschec ( 1963) with minor modifications. Their primary distinction from other media is a high saccharose content (8 % ). Besides, the blood for the serum is drawn into a 10% solution of trypsin (see further thesis J. Waldman, to be published). For the isolation of T strains, we have adopted the advice of M. C. Shepard (1965) and adjusted the pH of the medium to 6. The plates are incubated anaerobically in hydrogen with 20% COz. For other mycoplasma, the pH of the media is 8 and the plates or broth cultures are incubated anaerobically with 5 % COz, except for M . pneumoniae which is also incubated aerobically. Colistinum (80mgr/600 ml medium) is added in part of the media to suppress the growth of contaminating bacteria (colistinum methane sulfonate) .
The Colours and Dresses of Racism in America
The monograph argues that American racism has two colours (white and black), not one; and that each racism dresses itself not in one clothing, but in four: (1) “Minimal” negative, when one race considers another race inferior to itself in degree, but not in nature; (2) “Maximal” negative, when one race regards another as inherently inferior; (3) “Minimal” positive, when one race elevates another race to a superior status in degree, but not in nature; and (4) “Maximal” positive, when one race believes that the other race is genetically superior. The monograph maintains that the needs of capitalism created black slavery; that black slavery produced white racism as a justification for black slavery; and that black racism is a backlash of white racism. The monograph concludes that the abolition of black slavery and the civil rights movement destroyed the social and political ground for white and black racism, while the modern development of capitalism is demolishing their economic and intellectual ground.