ORGANIC ADAPTATION 343 



Among the various classes of antibodies are the antitoxins 

 that neutralize the poisonous products (toxins) of certain Bac- 

 teria; the precipitins that act upon foreign proteins of bacterial 

 or other origin; the lysins that actually destroy foreign cells; and 

 the opsonins that render Bacteria vulnerable to the attacks of 

 the phagocytes. 



Various specific antibodies may be naturally present in the 

 blood — a part of the heritage — so that an individual is immune 

 to certain diseases due to pathogenic organisms. Or the anti- 

 bodies may be produced in response to the parasites themselves, 

 and the individual acquires immunity only after undergoing the 

 disease. Again, immunity may be artificially acquired by various 

 means, such as vaccination, which stimulate the production of 

 antibodies so that the individual is prepared in the event of an in- 

 fection. 



Indeed, the subject of immunity has become a science in itself 

 (immunology) within the past few years — a science which has as 

 its fundamental basis the investigation of the marvelous power of 

 adaptation of protoplasm as exemplified in coping with disease- 

 producing parasites, and even with those ultramicroscopic agents 

 of disease, the so-called filterable viruses, such as produce 

 smallpox, measles, rabies, etc. The viruses are so small that they 

 pass through porcelain filters and, in one case at least, consist of a 

 single protein molecule. But they have the power to multiply 

 when in the protoplasm of host cells and so exhibit one funda- 

 mental characteristic of life. The viruses appear to be on the 

 border line between the lifeless and the living but to include them 

 with the latter would necessitate an extension of our present con- 

 ception of life. Their further study is certain to be of immense 

 practical and theoretical importance. 



C. Individual Adaptability 



We may now turn to a survey of the highest expression of ad- 

 aptation evolved by Nature, which appears as tropisms and other 

 elements of behavior in the lower organisms, gains definiteness 

 and content as we ascend the animal series, and becomes the basis 

 of intelligence and all that the mental life of Man involves. It 

 is the adaptation which renders Man essentially superior to adapta- 

 tion — enables him to a large extent to control, instead of being 

 controlled by his environment. 'It seems that Nature, after elab- 



