ADRENALS 673 



such transplants according to the age of the animal (Marine and 

 Manley). In young rabbits, the transplants grow rapidly if the 

 spleen is removed at the time of transplantation, while in sexually 

 mature rabbits they do not grow and often undergo gradual absorp- 

 tion. Likewise, transplants which have grown rapidly in young 

 animals decrease in size after adult life is reached, indicating that 

 the function of the spleen is more necessary in young than in older 

 animals ; or that its function is more easily and completely assumed 

 by other tissues, probably the bone marrow, in adults. A further 

 and very suggestive fact, is that a subcutaneous spleen graft which 

 has ' taken,' but is not growing, in a young animal whose spleen has 

 not been removed, can be made to grow by removal of the spleen. 

 These results indicate that splenic insufficiency is a necessary con- 

 dition of growth of a splenic transplant, just as thyroid insufficiency 

 is a necessary condition of growth of a thyroid transplant. The 

 stimulus to growth in the one case, as in the other, must be assumed 

 to be a chemical stimulus transmitted through the blood, and not 

 dependent upon the nervous system. 



The salivary glands may be extirpated without any sensible change 

 being produced in the normal metabolism. It has been stated how- 

 ever, that the secretion of the gastric juice is diminished. It has been 

 supposed that this may be due to the absence of a hormone (p. 404) 

 normally produced in the salivary glands. A temporary increase in 

 the gastric secretion is said to be caused when extracts of the glands 

 of normal dogs are injected into the veins or into the peritoneal cavity 

 of dogs deprived of their salivary glands (Hemmeter). But later 

 experiments contradict the theory of the existence of a hormone in the 

 salivary glands, which stimulates the secretion of gastric juice. The 

 average rate of secretion into a Pawlow gastric pouch (p. 403) was not 

 diminished in dogs after extirpation of the glands (Swanson.) 



Extracts of nervous tissue (sciatic nerve, white matter of brain, and 

 spinal cord, but especially grey matter of brain) cause, on injection into 

 the veins, a decided fall of arterial blood-pressure, which soon passes 

 off, and can be renewed by a fresh injection. The fall of pressure is 

 due to direct action upon the bloodvessels of a depressor substance in 

 the extracts, and not to the action of vaso-motor nerves. It can be 

 obtained after section of the vagi. 



Extracts of muscular tissue also cause a distinct though transient 

 fall of pressure, but not so great a fall as in the case of extracts of 

 nervous tissue. Saline decoctions of other tissues (testis, kidney, 

 spleen, pancreas, liver, mucous membrane of stomach and intestine, 

 lung, and mammary gland) all produce a fall of blood-pressure (Osborne 

 and Vincent). The same is true of bone marrow (Brown and Guthrie; 

 Figs. 218, 219). It must be repeated that there is no evidence that 

 these depressor substances are specific internal secretions in the same 

 sense as epinephrin. 



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