106 ORGANIC DEPENDENCE AND DISEASE 



limitations of time. But we have little except inference to 

 build on in applying this statement to those early periods 

 of geological history in which various types of life were 

 establishing themselves and with which we have been es- 

 pecially dealing. 



Two reasons restrain us from attempting to ascribe such 

 high influence to microorganic disease in the early life 

 periods of the earth : 



1. Inadequate records. 



2. Protozoan parasitism functions essentially as a chem- 

 ical attack upon the tissue and proteid contents of the cell 

 of the host for purposes of nutrition, and results in injury 

 to such tissue by exudation of active poisons. In metazoan 

 parasitism the injury thus caused, if any, and the adjust- 

 ment in any cases, are mechanical and due to the functional 

 mechanism of the parasite. 



The essential conception of germ disease is the invasion 

 of the cell by another cell, in which the invader strikes right 

 at the heart of the host by the attack upon the molecular 

 constituents of the protein, inclusive of the chromosomes 

 which are the recognized carriers of the traits which we 

 characterize as individuality and heredity. It is, in other 

 words, the attack of the individual cell on the individual cell, 

 in which the invaded cell must rouse itself to its full power 

 of opposition by the development of greater molecular 

 strength and more resistant cell tissue. 



Of such procedures we can learn only from the living 

 world. 



The conception that the progress of life by evolution is 

 the path which germ disease has permitted and which might 

 have been otherwise if not prevented, would seem to tear to 

 tatters the obvious plans and purposes laid down in the 

 scheme of nature — like a carpet that has been so eaten by 

 moths that the pattern is gone and with it the purpose or 

 the thought of its maker. We therefore emphasize the dis- 

 tinction between protozoan and metazoan parasitism and 



