MILLIPORE FILTERS STUDIED IN ISOLATION AND IN VITRO BY TRANSMISSION ELECTRON MICROSCOPY AND STEREOSCANNING ELECTRON MICROSCOPY

1. 1. Millipore filters were studied by light microscopy, transmission electron microscopy and stereoscanning electron microscopy. 2. 2. The filters are composed of cross-linked filaments forming pores which vary greatly in size. 3. 3. The structure of the filter is distorted by ethanol pre-treatment for in vitro studies and by the ethanol dehydration process. It is recommended, therefore, that caution be exercised in interpreting any results based solely on ethanol treated Millipore filters. 4. 4. Sections of filters examined by electron microscopy after routine preparative treatments do not show clearly defined pores. In contrast, those filters placed either on the endoderm or between the ectoderm and endoderm of the chick embryo show clearly defined pores. It is concluded that when fluid from the tissues lines the pores and becomes stained the filter structure is visible. 5. 5. Cellular extensions and cytoplasmic droplets may also be seen in these filters. © 1969.