Antimicrobial substances and chick growth promotion: Comparative studies on selected compounds in vitro and in vivo

1. Antibacterial activity of selected compounds in vitro and their ability to promote growth when added to the diet of chicks were not correlated.

2. The difference in growth‐promoting activity between streptomycin, which was active, and kanamycin which was not, was not related to their effects on the flora adhering to the wall of the crop, jejunum or ileum, to their relative toxicity to the chick nor to differences in their stability in the diet.

3. When low concentrations ofkanamycin or streptomycin were given, the antibiotic was concentrated in the caecal contents. In contrast, penicillin was undetectable in the caeca of birds given high concentrations of benzyl penicillin.

4. In chicks given benzyl penicillin, the numbers of Streptococcus faecium increased at the expense of Strep, faecalis. This probably resulted from changes in the crop flora.

5. Birds given high dietary concentrations of benzyl penicillin showed improved weight gains, in spite of increased numbers of Escherichia coli in the small intestine.     

The hen's egg: Relationship of mean strain energy at shell fracture to shell compression speed,the nature of the compressing body and the location on the shell of the point of contact

1. The mean energy, E_f, required for fracture of an egg shell at its equator by a flat plate is known to depend on shell compression speed, v_m, for speeds in the range 20 μm/s to 2.lb5 mm/s; analysis of published data shows that E_f bears a linear relationship to log (v_m ) throughout the industrially important speed range from 20 μm/s to 1.lb1 m/s, increasing from 1.lb3 to 5.lb0 mJ.

2. At lower speeds down to 2 μm/s E_f is constant.

3. E_f is reduced if the flat plate is replaced by a sphere or cylinder; the greater its curvature, the smaller E_f.

4. E_f for the narrow pole is greater and for the broad pole smaller than that for the equator but these differences may be due in part to . systematic differences in shell thickness as well as curvature.     

Biochemical,physiological and production indices related to fat metabolism in the laying fowl at various stages of physiological development

1. The significance of fat accumulation during physiological development of layers was studied using White Leghorn x Australorp pullets from 12 weeks of age.

2. Liver fat, carcass fat, liver weight and body weight increased markedly at the onset of sexual maturity.

3. Within the liver, the protein to DNA ratio did not alter significantly during development; glycogen was not consistently depleted by egg production.

4. Liver fat content was significantly correlated with carcass fat, liver weight and DNA concentration, and plasma total lipid and cholesterol, independent of stage of development; with body weight, liver protein, moisture, and protein to DNA ratio, excluding the period prior to commencement of sexual maturation; and with plasma phospholipid during lay.

5. Obesity was a feature of faster growing fowls which matured earlier, consumed more, utilised food less efficiently for egg production and produced fewer saleable eggs.     

Life below the ross ice shelf, antarctica

Samples and observations under 420 meters of ice and 430 kilometers from the open sea on the Ross Ice Shelf at a water depth of 597 meters revealed an unusual assemblage of benthic organisms. Scavenging amphipods, an isopod, and fish were present but a living infauna was absent. The observations may be accounted for by sampling or spatial bias, or by extremely low or fluctuating trophic resources.