Elizabeth Chant Robertson

Higher resistance of rats fed casein than those fed vegetable proteins.

Conclusion Rats fed a diet containing casein have a considerably higher resistance to enteritidis infections (I.P.) than controls fed either wheat gluten or soy bean flour.

Increased Resistance of Rachitic Rats fed Irradiated Food.

Summary Of 89 rats fed a rachitic diet including non-irradiated muffets, 5% survived a per Os enteriditis infection, as compared with 30% of 94 rats fed the same diet including irradiated muffets. Therefore we conclude that the use of irradiated whole wheat (muffets) in a rachitogenic diet fed to rats increases their resistance against infection.

Difficulties in the Use of Brachycardia Method of Assaying Vitamin B1

Using the brachycardia method as described by Harris and Leong, 1 we have attempted to assay vitamin B1 hydrochloride (Merck),∗ and the international standard of vitamin B1. Young piebald rats from our own rat colony, when 45 to 50 gm. in weight, were put on a vitamin B1-free diet made up of crude casein 18%, McCollums Salt Mixture (No. 51) 4.5%, sugar 61.5%, cod liver oil 1%, and autoclaved yeast 15%. The latter was strongly alkalinized, autoclaved at 15 lb. pressure in thin layers for 5 hours, and then neutralized and ground. The rats were all kept in wire cages, having meshes 5/8 in. square, in order to prevent possible coprophagy. After about 12 days on the diet, the rats were weighed daily. When the body weights were constant, electrocardiograph records, using a standard Cambridge electrocardiograph, were taken each day. When the heart rate came down to 370 to 390 per minute, the rat was given a single dose of vitamin B1. A solution of the vitamin Bi hydrochloride was made up daily in distilled water, and the international standard was weighed dry. The dose was mixed with a little autoclaved yeast and then fed to the rat. At least 5 rats received each dose, and they usually ate it within one to 1½ hours. If they took longer than 4 hours, the results were often unsatisfactory. Daily electrocardiograms were taken on each rat at about the same time each morning. The rats were held gently by hand while the records were being made and very rarely struggled or squealed during the process. Great care was taken not to hold the skin tightly, and there was no possibility of asphyxia complicating the results.

Relation of Humidity to Resistance to Infection in Rachitic Rats

McDowell, 1 showed that the mortality following an intraperitoneal injection of pneumococci in adult rats kept for 2 weeks in a room at a temperature of 84°F., was much higher when the relative humidity was 84% than when it was 44%. When the temperature varied between 65° and 72°F., a larger percentage of all the rats died, but variations in the humidity had no effect. Kligler and Olitzki 2 reported very similar results with adult mice, but, in their work, the exposure to the special environment took place only 3 days before and for one month after an oral infection with Salmonella enteritidis. At 68°F. differences in humidity did not influence the mortality rate. The following experiments differ from those above mentioned in that (1) young rats were used; (2) a rickets-producing diet was fed; (3) the exposure to the various temperatures and humidities was for the 4 weeks preceding infection; (4) the effect of air drawn from inside and outside the building was compared. Litters of rats which had just been weaned were divided into 4 equal groups, and put in divided cages in 4 closed wooden boxes through which the conditioned air was passed. The air for 2 of the boxes, one high and one low humidity, was drawn from outside the building, and that for the other 2, also one high and one low humidity, was drawn from the large animal room which housed the boxes. The air for each pair of boxes was drawn from its source by a pump and passed through a tank of anhydrous crude calcium chloride, through an electric heater, and into the box. The heaters were under the control of thermo-regulators in the boxes, and the temperature of the conditioned air surrounding the rats was kept constant to within a few degrees.

Increased resistance of rachitic rats exposed to sunlight through Vita glass.

Summary Of 41 rats fed a rachitic diet and exposed to sunshine through Vita glass, 61% survived a per os enteriditis infection, as compared with 28% of 32 similar rats exposed to sunshine through plain or ordinary glass.