172 ON VARIABILITY AND ADAPTATION 



the members of the association. That journal, like the associa- 

 tion, had but a brief existence. In its thirty-first number, 

 Geheimrath Dr. Mettenheimer published his observations on 

 myelin, noting its power of double refraction. The observa- 

 tions were so important that the elder Beneke, in 1862, reprinted 

 the article in its entirety. But this happened in a monograph 

 whose title, " The Presence, Distribution, and Formation of the 

 Constituents of Bile," did not in the least suggest that it was 

 concerned largely with this subject of myelin. Thus it is that, 

 reviewing the literature for the next forty-four years, I have 

 failed to come across a single reference to Mettenheimer's 

 work, while Beneke's, after a year or two, appears similarly 

 to have passed into oblivion until quite recently, when, with 

 filial piety, the younger Beneke drew renewed attention to his 

 father's work. In the meantime workers in different branches 

 of biologic science made, as they thought, the independent 

 discovery of this property of myelin — Apathy, in 1889-90, 

 working on the histology of the nervous system, G. Quincke, 

 the physicist, in 1894, Miiller of Marburg in 1898, and Kaiserling 

 and Orgler of Berlin, later in the same year ; and of these, from 

 their writings, each seems to have been supremely ignorant 

 that any one had been before him in making the observation 

 that myelin is doubly refractive. 



That all substances affording myelin forms can be shown 

 to be doubly refractive I greatly doubt, or, more accurately, 

 I would say that there are substances, such as the lecithins, 

 capable of affording myelin forms of the simplest type with 

 which so far I have been unable to gain doubly refractive 

 globules. 1 I shall have something to say later regarding these 

 apparent exceptions. 



I have here tabulated the distribution of Virchow's myelin 

 in the organism as it has been recorded by various observers : 



1 Since delivering this address I have found that at least one lecithin (from 

 egg yolk) gives with water exquisite doubly refractive figures, and that after 

 repeated solution in chloroform and precipitation with acetone, a procedure 

 which should remove any dissolved cholesterin. This is in opposition to 

 Beneke's statement that egg lecithin completely purified from cholesterin gives 

 no myelin figures. It is possible that Beneke is correct, but if so the process of 

 separating cholesterin from lecithin must be very difficult. 



