CH. XXIX.] ELECTRICAL CHANGES IN GLANDS 473 



mian follicles are examples of this kind of gland. Some glands, like 

 the pancreas, are of a mixed character, combining some of the char- 

 acters of the tubular with others of the racemose type; these are 

 called tululo-racemose or tubulo-acinous glands. These glands differ 

 from each other only in secondary points of structure, but all have 

 the same essential character in consisting of rounded groups of 

 vesicles containing gland-cells, and opening by a common central 

 cavity into minute ducts, which ducts in the large glands converge 

 and unite to form larger and larger tubes, and at length open by one 

 common trunk on a free surface. The larger racemose glands, like the 

 salivary glands, are called compound racemose glands. 

 On internal secretions, see p. 328. 



Electrical Variations in Glands. 



These have been studied in many glandular organs, but especially in the 

 salivary glands and skin. 



In the subraaxillary gland the hilus is electro-negative to the external surface 

 of the organ ; a current therefore passes from hilus to surface through the galvano- 

 meter. If the chorda tympani is stimulated by rapidly interrupted shocks, the 

 surface becomes still more positive. This is the opposite to what occurs in a 

 muscle ; there the current of action is in the reverse direction to the demarcation 

 current ; the change in the gland is a positive variation in the arithmetical sense. 

 This is abolished by a small dose of atropine ; stimulation then causes a small 

 negative variation which is abolished by a larger dose of atropine. 



If, before atropine is given, slowly interrupted shocks are used, or rapidly 

 interrupted shocks too weak to excite secretion are employed, the electrical response 

 of the organ is a negative variation. The same is true for stimulation of the 

 sympathetic. Single induction shocks applied to the chorda tympani cause a 

 diphasic variation, first the surface of the gland becoming more positive and then 

 the hilus. 



The two changes are believed to be due to the fact that secretory nerves are of 

 two kinds : anabolic, which increase the building up of the glandular protoplasm ; 

 and katabolic, which increase the disintegrate side of metabolism, and so lead to 

 secretion. 



It is important to remember the existence of the skin currents, for they interfere 

 with any attempt to determine the electrical change in muscles through the intact 

 skin. This interference will naturally be greater, the richer the portion of skin is, 

 in secreting glands. 



The most satisfactory work on skin currents is that recently carried out by 

 Waller. He speaks of them as glandular and epithelial, and regards them as 

 important signs of life here as in other tissues (eye, muscle, nerve, plant tissues, 

 etc.) which he has studied. He has worked with the skin of the frog, cat, and 

 other animals, including fresh human skin obtained from surgical operations. The 

 skin may be excited either directly or indirectly through the nerves that supply it. 

 The main results obtained are very simple, and are also true for mucous membranes, 

 and such epithelial structures as the crystalline lens. The normal current of 

 unexcited living skin is ingoing. The normal response of excited skin is outgoing. 

 This is explained in the following way : In a passive mass of living animal 

 material acted upon by its environment, there must be most change occurring on its 

 surface, a point on the surface will therefore be electropositive to any point in the 

 interior. If the same mass is excited, chemical changes will be greater in its 

 interior than at the surface ; hence internal points become less electronegative than 

 they were before, or even electropositive in relation to the external surface, hence 

 the current of action through the mass of skin is outgoing, and will therefore pass 

 through the galvanometer from the external to the internal surface. 



