I am privileged to-day in having been invited to give this address, but I feel that I am particularly privileged also in that, so far as I can discover, this is the first occasion in the annals of the Royal Society of Edinburgh on which a veterinarian has been asked to address the Society on matters concerning the diseases of animals.

The Veterinary profession has long been recognised as a handmaid of Agriculture but, like her sister profession Medicine, her services, until comparatively recently, have been based on knowledge acquired by long experience derived from trial and error, as distinct from planned experiment based on scientific principles.

The Rowett Institute for research on animal nutrition had its origin under a scheme for promoting scientific research in agriculture adopted by the Development Commission in 1911.

The Governing Body, which originally consisted of an equal number of members appointed by the Court of the University of Aberdeen and the Governors of the North of Scotland College of Agriculture, was constituted in 1913. Within recent years it has been expanded to include persons nominated by the Secretary of State for Scotland, the Royal Society, the Royal Society of Edinburgh, the Agricultural Research Council, and the Medical Research Council. Research work was begun in temporary accommodation in Marischal College in 1914, under the direction of Dr John Boyd Orr—now Lord Boyd-Orr—who continued as Director until his retirement in 1945.

A system of twelve stages of expansion from one primary monotypic genus is described and elaborated, using as two correlated parameters the rate of x 1·5 for the number of new monotypic genera arising (rGi) when the rate of X 2·0 is taken for the increase in generic size or numbers of species within any one genus (rSz). Too much stress should not be read into the precision of the positions indicated for known numerical data; an approximate fitting is all that can be reasonably expected even if these theoretical expansions are something like the historical truth.

The form and structure of the uterus of the albino laboratory rat are described. Cyclical vascular changes are noted, and attention is drawn to the presence of spiral arteries in the endometrium. A common lower cervical canal is described.

The common strain and six specialised strains of Phytophthora infestans have been employed in testing potato varieties and seedling progenies bred from the wild species S. demissum for resistance to the disease. Resistance, due to the hypersensitive condition of the protoplasm, is manifested in the presence of major genes, and four such genes have been identified, viz. R1, R2, R3 and R4. Each gene induces in the plant a hypersensitive response to infection with the common strain and with a particular group of specialised strains of the parasite. The genes are inherited independently in simple Mendelian fashion, but in the segregations three different types of deviations from standard disomic ratios occur due to (a) unpaired chromosomes, (b) incompatibility factors, and (c) partial autosyndesis. A series of minor genes modify the phenotypic expression of the major gene system and so differentiate grades of hypersensitivity or of susceptibility as the case may be.

The common strain of P. infestans appears to be a population persisting at an equilibrium determined by host range and environmental conditions. Mutations frequently occur, but new forms survive only when host genotypes, to which they are specially adapted, are available.

The mature Ptinid sperm examined under the light microscope is found to be specialised in that the chromatin is not contained within a sperm head but is distributed along a central axis. The migration of chromatin resembles that found in Coccids by Hughes-Schrader (1948). Surrounding the axis is a more flexible helical membrane extending the whole length of the sperm.

Under the electron microscope the membrane appears to consist of eighteen or twenty thin fibres and two thick fibres with striated sheaths. Near the posterior end of the membrane the fibres are surrounded by a ring. The structure is simpler than that of mammalian and avian sperms examined by other workers with similar techniques. Under the electron microscope, stages in the migration of chromatin in the immature sperm show a number of discrete opaque bodies which may be chromosomes. The approximate dimensions of the various structures are given.