THE SYMPATHETIC SYSTEM 311 



the pharmacological action of the endocrines, we are 

 struck by the fact that while they all act more or less on 

 the nervous systems of the vegetative life, certain ones 

 have an elective action on one or part of one system. 

 Suprarenalin, the product of the medullary portion of 

 the suprarenal capsule is a good example. Outside of the 

 sudoriferous glands, suprarenalin will cause symptoms 

 identical to the phenomenon produced by stimulation of 

 the true sympathetic. This is not to be wondered at, if 

 we remember that morphologically the sympathetic and 

 chromaffin cells have the same origin. 



Chromaffin cells, or adrenal cells, or sympathetic cells 

 being of common origin, have a similar function; for this 

 reason the chromaffin system or system of the paraganglia 

 must be classified with the true sympathetic and together 

 with it, belongs to the vegetative nervous system. The 

 chromaffin hormone is not the only one of these substances 

 which acts electively on the nervous systems of the vegeta- 

 tive life. All the glandular secretions of the endocrines 

 act more or less electively on part or the whole of one of the 

 systems. The action is, however, so complex that we 

 as yet do not know definitely how they act. At the 

 present stage of our knowledge, we must limit ourselves to 

 certain definite hormones. 



According to their action on the nervous systems of 

 vegetative life internal secretions can be divided into two 

 groups ; on one side the secretions of the thyroid and pitu- 

 itary; on the other, the secretions of the cortex of the 

 suprarenals and of the pancreas. 



The internal secretions of the thyroid and pituitary act 

 particularly as stimulants of the true sympathetic, but 

 they only act on certain portions of this system. The 

 thyroid secretions stimulate the superior portions of this 

 system, (cervical and thoracic portion), while pituitrin 



