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SCIENCE 



[N. S. Vol. XXXVI. No. 923 



but in those which are, the effects are strik- 

 ing. Their regulation is of the same gen- 

 eral nature as that exercised upon involun- 

 tary muscle, but it influences the chemical 

 activities of the gland-cells and the out- 

 pouring of secretion from them. By means 

 of this regulation a secretion can be pro- 

 duced or arrested, increased or diminished. 

 As with muscle, a suitable balance is in this 

 way maintained, and the activity of the 

 glands is adapted to the requirements of 

 the organism. Most of the digestive glands 

 are thus influenced, as are the skin-glands 

 which secrete sweat. And by the action of 

 the nervous system upon the skin-glands, 

 together with its effect in increasing or 

 diminishing the blood-supply to the cutane- 

 ous blood-vessels, the temperature of our 

 blood is regulated and is kept at the point 

 best suited for maintenance of the life and 

 activity of the tissues. 



The action of the nervous system upon 

 the secretion of glands is strikingly exem- 

 plified, as in the ease of its action upon the 

 heart and blood-vessels by the effects of the 

 emotions. Thus an emotion of one kind — 

 such as the anticipation of food — will cause 

 saliva to flow — ' ' the mouth to water ' ' ; 

 whereas an emotion of another kind — such 

 as fear or anxiety — will stop the secretion, 

 causing the ' ' tongue to cleave unto the roof 

 of the mouth," and rendering speech diffi- 

 cult or impossible. Such arrest of the sali- 

 vary secretion also makes the swallowing 

 of dry food difficult: advantage of this 

 fact is taken in the ' ' ordeal by rice ' ' which 

 used to be employed in the east for the 

 detection of criminals. 



The activities of the cells constituting 

 our bodies are controlled, as already men- 

 tioned, in another way than through the 

 nervous system, viz., by chemical agents 

 (hormones) circulating in the blood. 

 Many of these are produced by special 

 glandular organs, known as internally 



secreting glands. The ordinary secreting 

 glands pour their secretions on the exterior 

 of the body or on a surface communicating 

 with the exterior; the internally secreting 

 glands pass the materials which they pro- 

 duce directly into the blood. In this fluid 

 the hormones are carried to distant organs. 

 Their influence upon an organ may be 

 essential to the proper performance of its 

 funations or may be merely ancillary to it. 

 In the former case removal of the inter- 

 nally secreting gland which produces the 

 hoi'mone, or its destruction by disease, may 

 prove fatal to the organism. This is the 

 case with the suprarenal capsules: small 

 glands which are adjacent to the kidneys, 

 although having no physiological connec- 

 tion with these organs. A Guy's physi- 

 cian. Dr. Addison, in the middle of the last 

 century showed that a certain affection, al- 

 most always fatal, since known by his name, 

 is associated with disease of the suprarenal 

 capsules. A short time after this observa- 

 tion a French physiologist, Brown-Sequard, 

 found that animals from which the supra- 

 renal capsules are removed rarely survive 

 the operation for more than a few days. 

 In the concluding decade of the last cen- 

 tury interest in these bodies was revived by 

 the discovery that they are constantly 

 yielding to the blood a chemical agent (or 

 hormone) which stimulates the contrac- 

 tions of the heart and arteries and assists 

 in the promotion of every action which is 

 brought about through the sympathetic 

 nervous system (Langley) . In this manner 

 the importance of their integrity has been 

 explained, although we have still much to 

 learn regarding their functions. 



Another instance of an internally secret- 

 ing gland which is essential to life, or at 

 least to its maintenance in a normal condi- 

 tion, is the thyroid. The association of im- 

 perfect development or disease of the thy- 

 roid with disorders of nutrition and inac- 



