THE AMERICAN NATURALIST 



[Vol. LV 



facts which lie at the very foundation of modem medical 

 theory and practice. I offer my apology in advance for 

 the lack of novelty in much of what I shall say. My only 

 justification is that a reconsideration of such familiar 

 knowledge gives one a good running start, so to speak, 

 for a leap into less known realms ; realms of great inter- 

 est to the embryologist, the cytologist, the student of 

 heredity and of evolution; regions in which lie hidden 

 the secrets of all life and form, of hereditary transmis- 

 sion, and of its converse, variation. 



It is clear that the phenomena which constitute the 

 field of immunology, although to-day viewed mainly from 

 the standpoint of infection and immunity, all have 

 broader biological aspects. They must in last analysis 

 be but heightened or specialized reactions of the funda- 

 mental processes which underlie all life phenomena. 

 They are but one of the many expressions of that deli- 

 cately balanced stereochemical system we call proto- 

 plasm, and they are inextricably interwoven in the ebb 

 and flow of metabolism, with such fundamental biologic 

 processes as growth, reproduction, irritability and adap- 

 tation. 



The physiologically minded biologist also inevitably 

 suspects close relationship between the reactions de- 

 scribed by the serologist and those manifested normally 

 in a living animal by that wonderful system of chemical 

 messengers or internal secretions, the hormones and 

 chalones, which, independently of the nervous reflex, can 

 stimulate or inhibit the activity of some organ in a part 

 of the body far distant from the source of the secretion 

 itself, and which undoubtedly play an important part in 

 development. There seems no reason to doubt that both 

 hormones and antibodies, for example, represent com- 

 plexes of atoms which were originally parts of body- 

 cells concerned in the normal metabolic processes. One 

 is extruded into the body fluids under the influence of a 

 usual and therefore normal stimulus, the other is the 

 product of an accidental stimulus resulting from disease 

 or other unusual condition. 



