46 ADAPTATION AND DISEASE 



botanist Stahl, 1 who a third of a century ago made the pioneer 

 observations upon what we now term chemio taxis. He noted 

 that the plasmodium of the myxomycete Fuligo, which at first 

 moves away from a 2 per cent solution of common salt, will 

 after a time (more especially if it has suffered from lack of water) 

 adapt itself to the solution, advancing its pseudopodia into it. 

 In other words, we have here a definite example of direct adapta- 

 tion during the lifetime of the individual, of change of habit in 

 these lower forms of life based upon physical changes in the 

 surface layers of the individual. The other consists of certain 

 observations of Musgrave and Clegg 2 upon intestinal amoebae. 

 They noted that these in the large intestine ingest selectively, 

 feeding upon only one of the many surrounding species of bacteria, 

 and that they could succeed in growing the amoebae on the 

 surface of agar plates if they effected a combined growth of the 

 amoebae and this one species of bacillus. By the gradual 

 addition of pure cultures of another bacterial species, with which 

 at first growth may not be possible indeed, with this form alone 

 afforded in the first place the amoebae died out the amoebae 

 at first became accustomed to the foreign forms, taking up 

 occasional individuals, until eventually they could be grown 

 in association with the second form alone, to the total exclusion 

 of the first. Here again we observe accustomance and progress- 

 ive utilization, and in no sense a chance variation. The same 

 observers note that inoculating amoebae plus bacilli into the 

 livers of rabbits they induced abscesses which yielded both 

 amoebae and bacilli, but inoculating the pus from the first 

 abscess into a second rabbit they now obtained abscesses con- 

 taining amoebae alone : in other words, the amoebae had now 

 adapted themselves to growth in and upon the tissues of the 

 rabbit an observation which throws light upon the frequency 

 with which entamoebae are obtained in a pure state from hepatic 

 abscesses in man. 



It will be seen that so far I have laid comparatively very 

 little stress upon the inheritance of these acquired characters 

 and the development of races or strains endowed with special 

 properties, the result of acquirement. I have done this pur- 

 posely, being convinced that the proper method of attack upon 



1 Botanische Zeitung, 1884, Nos 10 and 12, and Flora, Ixxvi., 1892. 247. 

 1 Reports of the Bureau of Oovernment Laboratories, Manila, 1904, No. 18. 



