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We have developed a method for measuring the average motion of a large number of biological objects or other small particles. The moving objects are recorded on a motion-picture film. We measure optically the cross correlations between suitable pairs of motion-picture frames. These measurements yield the average motion and the histogram of the displacement vectors of the moving objects, such as Rhizobia bacteria. The motion data are useful for biological and medical studies.

THE recent proposal1 to analyse shapes of biological objects by means of orthonormal functions opens up some interesting possibilities. In the work cited, a particular set of two-dimensional orthonormal functions synthesized from Walsh2 functions which take only the values +1 and −1 was used. As is well known, however, there is a vast number of other complete sets of orthonormal functions and, in fact, they could be constructed indefinitely. There are also standard linear methods for transforming from one set of orthonormal functions to another; these procedures can be realized as computer programmes.

A modification of the Kohler method is described which facilitates the measurement of the small retardations frequently found in minute biological objects.

IN a recent paper Ruska1 demonstrated experimentally the possibility of surpassing considerably the resolving power of an ordinary microscope by the use of an electron microscope. This high resolving power cannot be applied in biological research, however, without developing a new histological technique to prevent the destruction of the organic cells by the intense electronic bombardment.

Molecular Radiation Biology: The Action of Ionizing Radiation on Elementary Biological Objects. By Hermann Dertinger and Horst Jung. Translated by R. P. O. Huber and P. A. Gresham. Pp. x + 237. (Longman: London; Springer-Verlag: New York and Berlin, March 1971.) £3.00.

THE measurement of the optical thickness of biological objects, such as cells, in the living state can yield a value for the dry weight of the object1,2. Such measurements, however, are difficult to carry out with great precision. A method has previously been described3 for making very precise measurements of path difference in a reflecting interference microscope, using the principle of phase modulation. This principle can also be applied to the transmission microscope, and an experimental test of this has been made.

With the aid of the fluorescence microscope a redly fluorescing substance, which can be regarded as a porphyrine, is found in the pigment layer of the eyes ofHirudo medicinalis. As is well known, porphyrines are able to sensitize biological objects to light. It may be assumed, therefore, that the pigment in question plays a part in the perception of light stimuli.

Synthetic polymers, nanoparticles, and carbon-based materials have great potential in applications including drug delivery, gene transfection, in vitro and in vivo imaging, and the alteration of biological function. Nature and humans use different design strategies to create nanomaterials: biological objects have emerged from billions of years of evolution and from adaptation to their environment resulting in high levels of structural complexity; in contrast, synthetic nanomaterials result from minimalistic but controlled design options limited by the authors’ current understanding of the biological world. This conceptual mismatch makes it challenging to create synthetic nanomaterialsthat possess desired functions in biological media. In many biologically relevant applications, nanomaterials must enter the cell interior to perform their functions. An essential transport barrier is the cell-protecting plasma membrane and hence the understanding of its interaction with nanomaterials is a fundamental task in biotechnology. The authors present open questions in the field of nanomaterial interactions with biological membranes, including: how physical mechanisms and molecularforces acting at the nanoscale restrict or inspire design options; which levels of complexity to include next in computational and experimental models to describe how nanomaterials cross barriers via passive or active processes; and how the biological media and protein corona interfere with nanomaterial functionality. In this perspective article, the authors address these questions with the aim of offering guidelines for the development of next-generation nanomaterials that function in biological media. Published by the AVS. https://doi.org/10.1116/1.5022145