814 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



much to stimulate the secretion of milk, as to accelerate the outflow of 

 that which previously had been secreted and had collected in the alveoli 

 and ducts. This effect explains why the pituitary galactagogue should 

 have very little if any effect on the total production of milk or on the 

 total amount of fat and other constituents contained in it. Histological 

 examination of sections of a resting mammary gland and of the same 

 gland after administration of the pituitrin, bears out the above interpre- 

 tation of the action. Alveoli in the resting state will be found largely 

 distended with milk and the epithelium flattened against the basal mem- 

 brane, whereas alveoli from the gland after pituitary activity show small 

 shriveled-up alveoli, containing little milk, and with epithelium that is 

 well marked and stands out prominently from the basal membrane. 



These facts taken together indicate that pituitrin stimulates the mus- 

 cular fibers of the ducts of the mammary glands, thus squeezing out the 

 milk contained in them. Muscular fibers have been described as existing 

 between the basal membrane and epithelial cells, much in the same way 

 as they do in the case of the sweat glands. At least Schafer has suc- 

 ceeded in demonstrating in this position rod-shaped nuclei which prob- 

 ably belong to muscular fibers. 3 By their contraction, the milk in the 

 alveoli is expelled into the ducts. The observation of Maxwell, 53 namely, 

 that the alveolar contour of a lactating gland failed to show any change 

 when irrigated with pituitrin, is opposed to the foregoing view. It has also 

 been found that pituitrin stimulates the secretion of cerebrospinal fluid 

 and that this stimulation is independent of a rise in blood pressure. 



Recently Abel and Kuboto 54 have brought forward evidence to show that 

 the depressor effect of pituitrin and its stimulating action upon plain 

 muscle are not specific, but are due to the presence of histamine (/3-imi- 

 nazolethylamine) a substance we have seen to be produced by the de- 

 carboxylation of histidine (page 536). These authors have isolated the 

 depressor and the plain-muscle stimulant principle from the posterior lobe 

 of the pituitary in the form of a di-picrate. With regard to crystalline 

 form, solubility, melting point and the method of its isolation, this sub- 

 stance is identical with the di-picrate of histamine ; since the physiological 

 actions of the two substances are also the same their unity is believed to be 

 established. 



Pituitrin has a distinct effect on carbohydrate metabolism. After its 

 intravenous or subcutaneous injection, a marked lowering in the toler- 

 ance for sugar is observed (page 685), usually to such an extent that 

 glycosuria becomes established. Gushing and his pupils have concluded 

 that the posterior lobe contributes an autacoid which stimulates the utili- 

 zation of sugar in the body. Confirmatory evidence for this view is fur- 

 nished by the observation that mechanical stimulation of the posterior 

 lobe, such as is produced by puncturing it with a needle, is followed by 



