SECRETION PHYSIOLOGY. 335 



rent is able to transport these masses, while a more slowly 

 flowing secretion is not. Furthermore, in all probability the 

 saliva keeps on dissolving them as it carries them along and 

 hence becomes actually more concentrated, because it is in con- 

 tact with them really for a longer time than the more slowly 

 secreted saliva and not for a shorter time as Heidenhain thought. 

 Heidenhain made no endeavor to distinguish between the mat- 

 ters in suspension and those in solution. 



That any gland functions as a whole, as Heidenhain tacitly 

 assumes in his explanation, can not be maintained. 



The whole surface of the stomach, for instance, may be con- 

 sidered as one large gland. It has long been known that se- 

 cretion can ensue in one spot, and not in another. Heidenhain 

 himself, has called special attention to the marked differences in 

 the condition of the various alveoli in the salivary glands. Even 

 in the resting gland, here and there alveoli will be found posses- 

 sing the structural features of secretory activity."^ In the stomach 

 he remarks that some glands show changes on stimulation before 

 others, ^'^ and I have, myself, repeatedly observed glands in the 

 Newt's stomach close together in very different stages of activity. 

 Kiihne and Lea^"^ have observed this in the living rabbit's 

 pancreas, a portion only of the gland being normally active. 

 After pilocarpine all the alveoli passed into a condition of activit)'. 

 In the kidney the independence of the various tubules in se- 

 cretion has been remarked for the bird's kidney by von Wittich, 

 and for the mammalian kidney by Ribbert/'^ and by Dr. Herter 

 in conjunction with the author. Finally, in the case of the sali- 

 vary glands, Langley says that even on prolonged activity of the 

 chorda many alveoli show no change. ** This is due, in some 

 cases, to fibres escaping stimulation, fibres which leave the 

 lingual later than usual." This histological evidence appears 

 to me to be conclusive with reference to the idea that the gland 

 does not function as a whole, but that the individual alveoli in 

 the secreting gland may be here active, there passive. 



The physiological evidence that the foregoing is the true ex- 

 planation of Heidenhain's observation is hardly less conclusive. 

 We can easily obtain evidence that the secretion obtained 



