55 o SCIENCE PROGRESS 



entitle us to lose sight of the inherent differences between the 

 two ; it justifies us neither in calling the wave alive nor the 

 living organism " mechanical." Assimilation of matter is, 

 then, a vital characteristic, specific for livingness in a sense 

 in which neither affectability nor functional inertia is specific 



for it. 



But when we pass on to that vital property, the power to 

 produce anti-bodies, we encounter a property whose specificity 

 is absolute. This is a property known only within the last 

 few years ; and as it is the basis of immunity from the poison- 

 ings due to disease-producing micro-organisms, it is being very 

 carefully studied at the present time by workers in patho- 

 logical chemistry. 



Hardly any subject of biochemistry is so unsuited to 

 popular presentation, but the principle of it may be stated 

 as follows : if material foreign to the blood or tissues of an 

 animal be introduced into that animal's blood, then the body 

 cells proceed to elaborate a substance (anti-body) designed to 

 counteract or neutralise the foreign substance introduced. 



The substance introduced is known as an antigen ; the 

 substance produced as a vital response to the foreign stuff is 

 the anti-body. This is evidently a protective chemical pro- 

 cedure, or " mechanism," as it is called for short ; it is the 

 expression of the body's power of combating chemical insults 

 by chemical means. As a chemical process it is highly specific, 

 that is to say, the particular anti-body which neutralises the 

 poison of diphtheria, for instance, will not also antagonise the 

 poison of typhoid fever or of pneumonia. Each toxin is re- 

 sponded to only by its own specific antitoxin. Now this is 

 wholly without parallel or analogy in the world of the non- 

 living. It is characteristic of life alone, it is specific. Modern 

 biochemistry has, then, given us a new feature or differentia 

 of living matter, a power of protoplasm not recognised a few 

 years ago, not known to the men who regarded affectability 

 as the chief vital manifestation. 



The properties of reproduction and differentiation of tissues, 

 though recognised for a much longer time than the formation 

 of anti-bodies, are none the less confined to life alone. Non- 

 living matter behaves in no wise which could be construed into 

 regarding it as capable of reproduction or of progressive morpho- 

 logical differentiation. 







