30 BIOLOGY: GENERAL AND MEDICAL 



to recognize the most primitive forms in which it occurs, 

 being acquainted only with what are by comparison 

 highly evolved forms. 



REFERENCES. 



JOHN TYNDALL: "Floating Matter in the Air," N. Y., 1882. 



J. BUTLER BURKE: "The Origin of Life," N. Y., 1906. 



H. CARLTON BASTIAN: "The Modes of Origin of Lowest Organ- 

 isms, etc.," Lond., 1871. "The Nature and Origin of 

 Living Matter," Lond., 1905. 



