PROF. B. F. OSORIO TAFALL, National School of Biological Sciences, I. P. N., Mexico, has an article with the title "Naturaleza De Los Virus", in Ciencia of August 1943, which gives a very useful survey of the work done on viruses. While there is nothing added to our knowledge of the subject by this contribution, it provides an excellent historical review, and as it is written in a popular form, it will prove acceptable to many readers. Among the methods of studying viruses are ultra filters, colour tests (used to investigate psittacosis), photomicrography by ultra-violet light, the electron microscope, etc. New laboratory methods for diagnosing certain diseases caused by a virus which attacks both man and animals have been developed recently. Thus, Hertz described in 1942 how the allantois of the embryo of a chicken, when inoculated with the virus A and B of influenza, possesses the power of agglutinating the hæmatin, and this provides a simple test for detecting the virus of influenza in the throat and for determining the antibodies existing in the serum of the patient. The subject will be continued in a later issue of Ciencia.