ON THE TRUE AIM OF PHYSIOLOGY. 823 



capable of evolution. The organ, that much is certain, develops — that 

 is, it passes through a series of transformations before assuming its 

 final form. Any part of every organism will furnish the proof. But 

 what determines the final form during phylogenetic evolution ? I 

 answer, Function. With its assertion begins the differentiation of the 

 substratum of primitive beings. It is not the organ from which func- 

 tion derives its origin, but just the reverse. The functions create their 

 organs, or, to use a better definition, necessity determines the organic 

 form, which hence becomes hereditary, and ultimately in the embryo 

 of the higher animals in structure at least precedes function. 



When the embryo of the land-salamander, many months previous 

 to the normal time of its entry into the world, is taken out of the egg 

 and kept in water well supplied with oxygen, neither too warm nor 

 too cold, nor too dark, and amply fed with small living water-animals, 

 and if care is taken that the creature can not get out of the water, its 

 organism will change. It has to inhale the oxygen dissolved in the 

 water, not that of the atmosphere, like its parents breathing with lungs. 

 Its lungs therefore remain undeveloped, but by way of compensation 

 strong gills appear at each side of the head. The originally very feeble 

 function of respiration through gills, in conformity with the increased 

 demands of the growing body, creates a new organ, or calls forth one 

 possessed by its remote ancestors. The animal, moreover, feels the 

 necessity to swim, not to creep, like its terrestrial parents. Its four 

 extremities, therefore, become mere rudimentary appendages, while, 

 on the other hand, a vigorous rudder-tail develops. The function of 

 swimming calls forth fins, new organs which the parents lack. Thus 

 a substantially new animal is produced, which elsewhere does not ex- 

 ist, and which shows how through the development of new functions 

 new organs are formed, or, as it were, resuscitated. 



This principle applies not only to particular cases with artificially 

 created conditions but to all functions. All of them precede the organs 

 devoted to their exclusive service. All of them originate through 

 competition for the necessaries of life. At first a simple want is easily 

 satisfied by simple means, but gradually the organism is called upon to 

 meet numerous demands requiring complex contrivances through differ- 

 entiation. 



Instruments, apparatus, engines, are tools or organs invented by 

 human beings, because the wants of better food, better air, better water, 

 or the necessity of saving space and time, or of having means of com- 

 munication, protection etc., become more and more pressing among 

 them. They have, as it were, become part of the organism. Such 

 newly invented artificial organs as the spectacles, the watch, the shoe, 

 have all a long history of evolution. 



The kitchen, with all its large and small utensils for the cooking 

 and mixing and chemical preparation of the raw produce of the animal 

 and vegetable kingdoms, may be looked upon as one single digestive 



