23G CHAKLES n. STOCKARD AND G. N. PAPANICOLAOU 



by operation or the killing of the animal. In either case the pro- 

 cedure brought to a conclusion the observation or experiments on 

 the ovulation cycles in that specimen. Recognizing, on the 

 other hand, that no thorough investigation of the uterus and 

 vagina in the living female had been made, it occurred to us 

 that possibly oestrous changes might take place even though 

 they are so feebly expressed as not to be noticeable on casual 

 observation. The absence of an apparent oestrous or prooestrous 

 flow from the vagina of the guinea-pig has, as before mentioned, 

 no doubt been the chief reason for the general lack of knowledge 

 of the oestrous cycle. It was therefore determined to make a 

 minute examination of the contents of the vaginae of a number of 

 females every day for a long peroid of time, to ascertain whether 

 a feeble flow might exist although insufficient in quantity to be 

 noticed at the vaginal orifice or vulva. 



The observations were made by using a small nasal speculum 

 which was introduced into the vagina and the arms opened apart 

 by means of the thumb screw. The speculum permits an ex- 

 amination of the entire surface of the vaginal canal. In this 

 way the vaginae of a number of virgin females have been exam- 

 ined daily and smears made from the substances that happened to 

 be present in the lumen. 



By the use of such a simple method, it was readily deter- 

 mined after examining the first lot of animals for a few months 

 that a definite sexual period occurs lasting for about twenty- 

 four hours and returning with a striking regularity every fifteen 

 or sixteen days. During this twenty-four hour period the 

 vagina contains an abundant fluid which is for about the first 

 half of the time of a mucous consistency. The vaginal fluid then 

 changes into a thick and cheese-like substance which finally be- 

 comes slowly liquified and serous. This thin fluid exists for a 

 few hours and then disappears. Occasionally toward the end 

 of the process a sfight trace of blood may be present giving the 

 fluid a bloody red appearance, otherwise it is milk-white or 

 cream-color. 



According to the changes in appearance and consistency of the 

 vaginal fluid, one may distinguish four different stages. The 



