B. S. Schweigert

Amino Acid Composition of Morphological Fractions of Rat Livers and Induced Liver Tumors.

Summary 1. The perfused livers from adult rats fed either a basal diet containing 12% of casein or the same diet plus 4-dimethylaminoazobenzene for 4 weeks, and the liver tumors induced by this dye were fractionated into nuclear, large granule (mitochondria), small granule (microsome), and supernatant fluid fractions. The amounts of 17 amino acids were determined in the total proteins from the original homogenate and in each of the fractions. The importance of using perfused livers for these analyses was demonstrated experimentally. 2. When the basal diet was fed, the proteins from the nuclear fraction contained lower concentrations of histidine, tryptophan, phenylalanine, and cystine and a higher concentration of glycine than the whole liver proteins. The large granule proteins contained less histidine, the small granule proteins less methionine and glycine and more tryptophan, and the supernatant fluid proteins less tryptophan and more cystine than the proteins of the original homogenate. 3. The livers of rats fed the dye contained higher concentrations of glutamic acid in the nuclear proteins, arginine in the large granule proteins, and cystine and tryptophan in the supernatant fluid proteins than normal livers. 4. The proteins from each fraction of liver tumor contained less methionine and more cystine than the proteins in the corresponding

Dental Caries in the Cotton Rat

An experimental animal which is readily susceptible to dental caries has long been recognized to be the prerequisite for research in the causes and control of dental caries. Shaw, Schweigert, Mclntire, Elvehjem and Phillips (1) have given evidence that the cotton rat (Sigmondon hispidus hispidus) is much more susceptible to dental caries than any other experimental animal previously reported. The evidence presented indicates the opening of a fertile field for dental research. The method of production and the description of the carious lesions in the cotton rat are to be reported here.

Dental Caries in the Cotton Rat. V. Influence of Strain Variation on the Caries Susceptibility.

Summary A difference in susceptibility of different strains of cotton rats to dental caries has been observed and shown to be statistically significant. Preliminary results from second generation offspring indicate that their susceptibility is similar to that of the parent stock.

Dental Caries in the Cotton Rat. IV. Inhibitory Effect of Fluorine Additions to the Ration.

Summary Some inhibition of caries resulted when 45, 90, or 135 p.p.m. of fluorine were ingested as supplements to a sucrose basal ration. Depigmentation of the incisors appeared when 45 or more p.p.m. of fluorine were incorporated in the diet while mottling of the third molars occurred when 225 or more p.p.m. were fed. The ingestion of 225 or 450 p.p.m. of fluorine caused a 90%. decrease in caries incidence. Thus the amount of fluorine necessary to inhibit caries to this degree was sufficiently high to cause mottling of the developing teeth. The inhibitory effect of dextrin upon caries development could not be explained on the basis of its fluorine content.

Growth of Rats on Synthetic Diets Containing Limiting Amounts of Thiamine.

Summary Superior growth was obtained when synthetic diets containing various levels of thiamine were supplemented with sulphited liver extract. The addition of p-aminobenzoic acid and inositol to the synthetic ration also increased the rate of growth of rats receiving suboptimal levels of thiamine.