200 BIOLOGY OF DEATH 



toxins in determining the average duration of life is an 

 experimental inquiry into the effect of a bacteria-free, 

 sterile mode of life. Metchnikoff has sturdily advocated 

 the view that death in general is a result of bacterial 

 intoxication. Now a bacteria-free existence is not pos- 

 sible for man. But it is possible for certain insects, 

 as was first demonstrated by Bogdanow, and later con- 

 firmed by Delcourt and Guyenot. If one carefully washes 

 either the egg or the pupa of DrosopMla for 10 minutes 

 in a strong antiseptic solution, say 85 per cent, alcohol, 

 he will kill any germ which may be upon the surface. If 

 the bacteria-free egg or pupa is then put into a sterile 

 receptacle, containing only sterile food material and a 

 pure culture of yeast, development will occur and pre- 

 sently an adult imago will emerge. Adult flies raised in 

 this way are sterile. They have no bacteria inside or 

 out. Normal healthy protoplasm is normally sterile, so 

 what is inside the fly is bound to be sterile on that account, 

 and by the use of the antiseptic solution what bacteria 

 were on the outside have been killed. 



The problem now is, how long on the average do such 

 sterile specimens of DrosopMla live in comparison with 

 the ordinary fly, which is throughout its adult life as 

 much beset by bacteria relatively as is mau himself, it 

 being premised that in both cases an abundance of prop- 

 er food is furnished and that in general the environ- 

 mental conditions, other than bacterial, are made the same 

 for the two sets? Fortunately, there are some data to 

 throw light upon this question from the experiments of 

 Loeb and his associate Northrop on the duration of life 

 in this form, taken in connection with experiments in the 

 writer's laboratory. 



Loeb and Northrop show that a sample of 70 flies, of 

 the DrosopMla with which they worked, which were 



