DEATH AND THE DURATION OF LIFE 87 



cessation of respiration. We know that this result can 

 be brought about by mechanical violence, by poison, and 

 by disease, and, since nobody can escape all these agencies, 

 doubts have arisen whether we do not all die from injury 

 or disease, and whether such a thing as natural death 

 really exists. If there were no natural death it should 

 be possible to prolong life indefinitely if a complete pro- 

 tection against disease and accidents could be secured. It 

 is impossible to make such an experiment in a human 

 being, since our intestine and our respiratory tract can 

 not be kept free from microorganisms. The problem has, 

 however, been solved for certain insects. A Russian 

 author, Bogdanow, invented a method of obtaining the 

 common house-fly free from all microorganisms, by put- 

 ting the newly laid eggs for a number of minutes into a 

 solution of bichloride of mercury of sufficient concentra- 

 tion. Most eggs were killed in the process, but some sur- 

 vived and these were free from microorganisms at their 

 surface. By keeping the eggs on sterilized meat and in 

 sterile flasks, the maggots leaving the egg could find their 

 food and develop into flies. A French author, Guyenot, 

 continuing the experiments on the fruit fly, raised 80 

 successive aseptic generations, and Northrop and the 

 writer have raised thus far 87 aseptic successive genera- 

 tions of the fruit fly on aseptic yeast. In these experi- 

 ments all possibility of infection, all chances of accidental 

 or violent death were excluded. To make sure that these 

 flies are absolutely free from microorganisms, their dead 

 bodies are transferred to culture media such as are used 

 for the growth of bacteria. If a common fruit fly is put 

 on such a culture medium, in 24 hours a rapid growth of 

 microorganisms develops, while the culture medium on 

 which our aseptic flies were put remained free from all 

 growth for years (or rather permanently). Aseptic fruit 

 flies, free from infectious disease and supplied with proper 

 food will, therefore, not escape death. These experi- 

 ments, then, indicate that higher organisms must die from 



