THE PITUITARY BODY 



rats before weaning (21-22 days) and in mice before an age of 

 18-20 days. The response is probably greater in animals a 

 few days older; one must avoid, however, any possible com- 

 plication due to normal "sexual maturity," which has been 

 known to occur in the rat at an age of 34 days, and in the 

 mouse at an age of 28 days. Animals may be of the same age 

 but differ markedly in development, which can be roughly 

 gauged by their body-weights. Under such circumstances, al- 

 though the same dose may be used, the ovaries of the heavier 

 and better-developed animals usually respond much better. 



The technique of injection is one of the most important 

 factors determining the ovarian response. Using an extract of 

 sheep pituitary. Maxwell (1934) gave the same dose divided 

 into four single injections daily, or into six injections daily for 

 4 days. In the group of immature rats receiving the latter 

 series of injections, the average weight of the paired ovaries 

 was 55 mg.; the paired ovaries of animals receiving single 

 daily injections weighed 25 mg.^^ By adding to the dissolved 

 extract, before injection, zinc sulphate equivalent to a dose of 

 3 mg. per day. Maxwell produced as great a change in ovarian 

 weight (weight of paired ovaries, 52 mg.) by administering 

 less than one-tenth of the dose used in the other experiments. 

 He considered that the zinc sulphate, altering the solubility 

 of the proteins present, caused a retardation in the absorption 

 of the hormone (which may be protein or protein-like). 

 Fevold and others (1933) have used tannic acid to alter ex- 

 tracts so as to retard their absorption. 



Probably the optimum time over which injections should 

 be distributed is 4-5 days. The ovaries should be removed 

 24-48 hours after the last injection.^^ If moderate doses of 

 gonadotropic hormone (pituitary) are used, the ovarian hy- 

 pertrophy is no greater, although injections are continued 



^5 In some strains of rats such an ovarian weight may be found in normal (unin- 

 jected) rats less than 30 days old. 



"Variations in a standardized technique of administering extracts must not be 

 introduced, although it is desired only to compare qualitative effects. 



