The Bacteriology of Pulp Slime

The occurrence of slime in various stages of the manufacture of pulp for paper stock constitutes a problem of increasing magni-tude. The effects of slime growths within pulp mills are well understood. Holes, characterized by a burnished and shiny margin are produced within the finished paper. In addition, accumulation of this thinly gummy material dispersed through the stock in finer particles injures the texture of the paper and is said even to interfere with proper sizing. The purpose of this study then was to determine if possible the cause of paper slime and also to ascertain certain facts dealing with its derivation. There have been many assumptions concerning the nature of the cause of this difficulty. Most of these guesses have been based upon the logical idea that some microorganism is an etio-logical factor but these hypotheses have not been founded upon experimental evidence. Algae, fungi including yeasts, and bac-teria have all been incriminated. If direct microscopical stains be made of this slime, a variety of forms will be found to be present, for the picture will include in addition to many finely divided but amorphous particles, a variety of bacteria. These are largely Gram-negative although some of them are Gram-positive. Those which are negative are usually three or four times as long as they are thick and are pleomorphic. A few mycelial threads of fungi will be noted but these are likely to be irregular in tinctorial reaction and may appear to be degenerating. An occasional yeast cell is evident. No algae are present. By process of exclusion then one is led by microscopic smear examination to seek the cause of slime produc-