770 THE ENDOCRINE ORGANS, OR DUCTLESS GLANDS 



in the mammary ducts so that the milk may freely flow out. By observ- 

 ing the rate of outflow during the injection of pituitrin, it will be found 

 that a remarkable increase occurs. After this increased secretion has 

 ceased, however, the injection of more pituitrin has no further effect, 

 indicating that the influence of the first injection must have been, not so 

 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 Schaf er has suc- 

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

 ably belong to muscular fibers. 60 By their contraction, the milk in the 

 alveoli is expelled into the ducts. 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. 



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 652), 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 

 a temporary glycosuria, which is said to be as pronounced as that fol- 

 lowing puncture of the diabetic center (page 672), provided glycogen is 

 present in the liver. The production of this carbohydrate autacoid would 

 appear to be under the control of the sympathetic nervous system, for it 

 has been found by Gushing and others that stimulation of the superior 

 cervical ganglion, which has been known for many years to be fre- 

 quently followed by glycosuria, has this effect only provided the posterior 



