The growth and variability in the body weight of the albino rat

For several years investigations have been in progress in the animal colony of The Wistar Institute for the purpose of ascertaining the environmental and nutritive conditions most favorable for the development of the rat.The very flourishing state of the colony at the present time seems to indicate that these investigations have solved the problem of the care and breeding of this animal, and that in future it will be possible to supply a 'standardized' type of rat for laboratory use.Growth records for the body weight of the albino rat have already been given by Donaldson ('06) and by Jackson ('13), but it seems worth while to publish additional data obtained from a study of a series of rats bred in The Wistar Institute colony in order to show the rapid and continuous growth of this animal in response to a particularly favorable set of environmental conditions.It is hoped that these records may also serve as standards with which the body weights of various strains of rats, raised under similar conditions, may be compared.The thirteen litters used in this study were taken from the general colony of albino rats kept as 'stock' supply.In choosing the litters care was taken to select only those in which the individuals were of good size at birth and appeared strong and vigorous.The animals used, therefore, represent the best stock in the colony.A random selection of any stock litters available for the purpose in mind was not feasible, as experience has shown that rats.that are small and weak at birth do not, as a rule, grow at a normal rate and that they usually die at an early 751