A method was dgscribedlr for measuring the chemotropic reaction of polymorphonuclear leucocytes in v i t r o . Leucocytes were observed with the microscope and their paths recorded as they approached bacteria or other sources of attraction. In measuring the reaction to these attracting bodies only the direction of the path was taken into account, not the rate of locomotion. It seemed possible, however, that leucocytes might respond to such attraction not only by moving toward its source but by traveling at increased speed. In this case it would be desirable to take account both of direction and of velocity of approach in measuring the chemotropic reaction.The point at issue has been touched on by previous observer^,^^ 41 who, however, did not make actual measurement to compare the rate of locomotion of leucocytes approaching a source of attraction with that of leucocytes moving at random. We have made such a comparison by means of a simple method which has been described by one of US.^ A minute clump of bacteria or of other particles is placed on a glass slide, where, after drying, it appears as a flat oval or circular body from 50 to 150 microns in diameter. A drop of blood, obtained by puncturing the finger, is placed on a coverslip, lowered *This investigation was aided by a grant from the Committee on Therapeutic
Synopsis The occurence of mercury-resistant pseudomonads in a seemingly well-preserved toiletry formulation is reported. Microorganisms identified as presumptive Pseudomonas aeruginosa have been isolated from a water-in-oil emulsion despite the inclusion of 0.007%phenylmercuric acetate (PMA) as preservative and also from an emulsion containing 0.002% PMA. Pseudomonads were capable of surviving in these emulsions for up to 3 and 12 months respectively. Culture studies confirmed that the isolates were initially resistant to maximum levels of PMA permitted in shampoos and hair creams according to EEC regulations. Microbial resistance of this nature emphasises the importance of strict attention to plant hygiene and good manufacturing practice.
Synopsis Although the role of micro-organisms located on the surface of the scalp is disputed by some authors, lipolytic organisms within the hair follicle may still be implicated in the causation of dandruff. Scale formation appears to be an adaptive response to threshold scalp irritation, taking the form of minimal parakeratosis possibly induced by products of lipolysis permeating thin regions of the horny layer. No single pathogen is yet clearly identifiable but effective anti-dandruff compounds display good antimicrobial activity against the typical lipolytic scalp microflora; this activity is retained in the presence of sebum and a feature of the most efficacious anti-dandruff agents is their good substantivity to the epidermal horny layer.
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