ACTIVE PRINCIPLES OF PARS NEURALIS 



concentration of pressor hormone in the pars intermedia in 

 terms of that in the pars neurahs was undoubtedly too low. 

 The pars intermedia probably contains one-fourth (and often 

 less) the concentration of oxytocic hormone found in the pars 

 neuralis; the concentration of pressor hormone in the pars 

 intermedia is probably less than one-sixth that in the pars 

 neuralis. 



"Units" of pressor or oxytocic hormone will be referred 

 to frequently in this chapter and in those succeeding it. The 

 international standard powder, which is almost everywhere 

 accepted as a standard, is arbitrarily considered to contain 

 2 units of whatever active principle is under investigation in 

 each milligram of powder. ■* According to Simon (1934), the 

 rat-pituitary contains about 0,8 unit of pressor or oxytocic 

 principle. Like others he found that the amount present was 

 not related to body-weight (100-300 g.). Activity, fasting, 

 adrenalectomy, etc., did not alter the total amount of the 

 hormones; however, a reduction in the amount of both prin- 

 ciples occurred if the supply of water in the diet was deficient. 

 Pak (1926) found that the amount of oxytocic hormone in 

 the rat's pituitary was not affected by thyroidectomy, 

 thyroid-feeding, or poisoning by "arsenic" or carbon mon- 

 oxide; the amount of the hormone was often reduced in 

 animals poisoned by mercuric chloride or diphtheria toxin. 

 In four of five animals faradic stimulation of the cervical 

 sympathetic appeared to cause an increase in the total 

 amount of the oxytocic principle. Simon and Kardos (1934) 

 estimated that the amounts of pressor principle in the pitui- 

 tary of the guinea pig, rabbit, and cat were 0.5-1.3 units, 

 1.3-2.5 units, and 5.6-13. i units, respectively; the amounts 

 of oxytocic principle appeared to be 0,4-1.0 unit, 0.6-1.5 



3 The international standard powder was prepared by Smith and McClosky 

 (1923-24). In the German literature the international unit is frequently called a 

 Voegtlin-Einheit. 



One mg. of international standard powder represents about 7 mg. of fresh pos- 

 terior lobe (ox). 



[321I 



