1244 PHYSIOLOGY 



degeneration. In a certain number of cases animals, especially if young, 

 have survived extirpation of the pituitary body. In these the operation was 

 followed by arrest of development the 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 

 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 

 recovered from the urine. It is possible that the polyuria, which is not 

 infrequently observed in association with head injuries or tumours of the 

 brain, may be occasioned by an increased escape of this material into the 

 general circulation. 



Extracts from the anterior lobe have no definite effect when injected 

 into the blood stream. Schafer found that the addition of the anterior 

 lobe of the pituitary body to the food of young growing animals caused 

 an increased rate of growth. In this experiment eight rats of a litter 

 were taken : four were fed with bread and milk to which the anterior lobes 

 of pituitary b6dies had been added, while the other four, which served as 

 controls, received bread and milk with a corresponding quantity of testis 

 or ovary. Later experiments have not however confirmed these results. 

 According to Mackenzie extracts of the pituitary body have a marked 

 excitatory effect on the secretion of milk by the mammary glands. 



It is evident that much further work is necessary before we can regard 

 the functions of the pituitary body as definitely ascertained. The evidence 

 we have at present would seem to point to the following conclusions : 



(a) The anterior lobe furnishes some substance to the circulation which 

 promotes growth, especially of the bony and connective tissues of the body. 



(b) The intermediate part surrounding the cleft between anterior and 

 posterior lobes, in addition to the production of some substance which is a 

 general excitant for unstriated muscle and produces diuresis, also furnishes 

 a colloid secretion which passes directly into the ventricles of the braiii and 

 may be assumed to have some influence on the growth or functions of the 



