(ESTRUS AND FECUNDITY IN THE GUINEA PIG 



DONALD B. TKESIDDEK 

 Department of Anatomy, Stanford Medical School 



This study was undertaken at the suggestion of Pro- 

 fessor Meyer, primarily for determining the numerical 

 relation between the corpora lutea of pregnancy and im- 

 plantations in the guinea pig. 



Most of the animals used in this experiment were pur- 

 chased from dealers, for it was impossible, in the short 

 time at my disposal, to obtain young animals of uniform 

 age and with the exception of a few guinea pigs raised 

 in our laboratory, only approximate ages were known. 



The guinea pigs were housed in a well-lighted, sunny, 

 heated room. Lantz, '13, reported that the optimum 

 temperature for the guinea pig is 65°. Draper, '20, 

 stated that they thrive best at temperatures between 50° 

 and 70° and found young animals extremely susceptible 

 to small changes in temperature; some of them dying 

 when the temperature was lowered permanently from 60° 

 to 58° F. However, I did not notice any marked differ- 

 ence in the behavior or condition of extremely young ani- 

 mals kept at a temperature of 50°. They showed every 

 sign of vigor and no animals were lost as a result of this 

 exposure. Indeed, I learned of guinea pigs kept in the 

 open in unheated pens, sheltered only from wind and 

 rain. These animals were said to thrive and to multiply 

 at the customary rate, but no records were kept. In my 

 own work I found that a few degrees above or below 50° 

 seemed to make no appreciable difference in the behavior 

 of the animals, and I hence am somewhat sceptical about 

 the marked susceptibility of the guinea pig to cold, so 

 often reported. 



The animals were fed dry alfalfa and barley daily and 

 green vegetables about twice a week. Many writers have 

 reported that guinea pigs did not do well on dry feed, 

 but it was my experience that, if fed an abundance of 

 water, they throve on alfalfa and barley alone. Since 

 they are subject to intestinal disturbances, it is of con- 

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