THE DUCTLESS GLANDS 1333 



by the transplantation of the gland from other animals into the brain 

 substance. 



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

 the different parts of the pituitary gland has been furnished by experi- 

 ments 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 mus- 

 cular tissues, such as the arteries of the lungs or heart, which do 

 not receive constrictor 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. It has been shown by Schafer that 

 the addition of the anterior lobe of the pituitary body to the food of 

 young growing animals causes 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 bodies had 

 been added, while the other four, which served as controls, received 

 bread and milk with a corresponding quantity of testis or ovary. 

 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. 



(6) The intermediate part surrounding the cleft between anterior 



