Recovery of oocysts of Cryptosporidium parvum using 142 mm diameter 1.2 μm pore size acrylic copolymer membrane filters was evaluated. A mean recovery efficiency of 25.5% for oocyst concentrations of about 200 in 10 1 was achieved, making this method a simple and relatively efficient procedure compared with current standard methods.

SummaryCrude tetanus toxin and toxoid were prepared by methanol precipitation. The toxin was purified by a combination of TEAE·cellulose and Sephadex G·200 chromatography at pH values less than 6· o. The toxoid was purified by DEAE· cellulose at approximately neutral pH values. The nature and amount of amino acids of the culture medium which had condensed with the tetanus toxoid proteins during detoxification with formaldehyde was determined.

Tetanus toxin has been extracted from culture filtrates by a single, cold methanol precipitation, followed by gradient elution on DEAE-cellulose. Immunoelectrophoretic evidence indicated that most of the bacterial protein was precipitated by the methanol. Selection of the toxin elution peak gave a product having only one immunoelectrophoresis precipitin line yet containing 50--60% of the Lf units applied to the column. The toxicity of this product was comparable to that found by other workers, using other methods of preparation. Sedimentation values of the concentrated pure toxin indicated heterogeneity in molecular aggregation and under conditions used no 4 S material could be found. Amino acid analysis of the tetanus protein is also reported.

The binding of formaldehyde with tetanus toxin under mild detoxificatIOn conditions (0 �1M phosphate buffer, pH 7� 0, O� 005-0� 06M HCHO, 20-37�C) has been studied quantitatively by using [14C]formaldehyde. When detoxification was followed with time (0� 005M HCHO, 37�C) the toxin showed a characteristic immediate drop in lethality (~80%), followed by a slower detoxification, whereas the combination of the HCHO was a more gradual process. When a fixed time period was used (5 days, 20 and 37�C) at least O' 02M HCHO was required to destroy the lethality of the toxin towards mice, and at this concentration approximately 60 moles of HCHO were bound per mole of toxin. Fractionation of a partially detoxified toxin indicated the presence of a range of molecular species with varying formaldehyde binding and lethality.