1192 PHYSIOLOGY 



pituitary body. In these the operation was followed by arrest of develop- 

 ment-rthe animals remaining in an infantile condition, small with an excess 

 of fat, and absence of sexual development. 



The most definite evidence we have as to the mode of action of the 

 different parts of the pituitary gland has been furnished by experiments on 

 administration or injection of the dried gland or its extracts. The posterior 

 lobe seems to be practically inactive, extracts made from this lobe having 



FIG. 550. Section of cat's pituitary body, passing through the cleft in the gland. 



(P. T. HERRING.) 

 a, pars anterior ; 6, cleft ; c, pars intermedia ; d, pars nervosa (posterior lobe). 



the same influence as extracts from nervous tissue generally. If, however, 

 the intermediate epithelial substance is included in the posterior lobe, 

 marked effects may be obtained from the intravenous injection. An 

 extract of the posterior lobe (including pars intermedia) produces, as was 

 shown by Schafer, a rise of blood- pressure and diuresis. The latter result 

 also follows administration of the posterior lobes by the mouth. Dale has 

 shown that the active principle exercises a direct excitatory effect on all 

 unstriated muscle, the effect being unaltered whether the nerve-supply to the 

 muscle be present or not. Thus it produces contraction of the blood-vessels, 

 of the intestinal muscle, and of the uterus, and will act upon muscular 

 tissues, such as the arteries of the lungs or heart, which do not receive con- 

 strictor impulses from the sympathetic system. The active principle is 

 much more stable than the other hormones we have already studied. It 

 is not destroyed by boiling, and after injection into the blood- stream can be 





