THE PITUITARY BODY 



under a pressure of 1-4 cm. of water and determining whether 

 or not the intra-uterine pressure is raised by the administra- 

 tion of extract. They declared that the quantitative assay 

 can be expressed in absolute "cat-units" (intravenous dose 

 about o.oi unit per kilogram cat). The same cat can be used 

 for several assays. 



The pressor principle {or its associated principles), i. The 

 pressor principle. — The assay of the pressor principle is of- 

 ten difficult because doses after the first may bring about 

 progressively smaller increases in the blood pressure (tachy- 

 phylaxis). The extract should, of course, be free of depressor 

 substances. To avoid tachyphylaxis the animal used for 

 assay should be carefully chosen; doses should be moderate 

 or small and must not be administered too frequently. The 

 anesthetic, if any, is also of importance. Hogben, Schlapp, 

 and Macdonald (1924) used the "spinal" cat into which they 

 gave an intravenous injection at intervals of i hour. They 

 recommended that the dose be about one-half that which 

 produces a maximal response. Swanson (1929) has used this 

 method or has used cats anesthetized by means of "Amytal"; 

 he made injections every 30 minutes. In the author's ex- 

 perience the method used by Kamm and his co-workers 

 (1928) is satisfactory. By this method the pressor response 

 to intravenous injections of small doses of posterior-lobe ex- 

 tract is determined every 15 minutes in dogs deeply anes- 

 thetized by "Chloretone." 



The determination of a vasoconstrictor effect by perfusing 

 an isolated structure such as the rabbit's ear cannot be made 

 quantitatively with posterior-lobe extracts. Moreover, such 

 a test object is relatively insensitive. Heymans (19-5) has 

 performed assays by determining the vasoconstrictor effect 

 of posterior-lobe extracts on the vessels of the perfused 

 head of the rabbit. 



1. The principle stimulating the musculature of the bowel. — 

 According to Simon (1933), this principle (which is often 



[3^4] 



