THE BACTERIAL NATURE OF MITOCHONDRIA 31 



been attributed to mitochondria seem to find their most 

 logical explanation in a conception of their bacterial nature. 

 Obviously, it became necessary to attempt experimental 

 and specific determination of the nature of these bodies. 

 It is evident that, if mitochondria could be induced to grow 

 independently of the cell, there could be no question regard- 

 ing their bacterial nature. 



The problem at the beginning was beset with a number 

 of difficulties. Bacteriological hterature contained a con- 

 siderable number of references to experiments on growing 

 bacteria in culture media planted with tissues from pre- 

 sumably health}', normal animals. These growths had 

 been thought to arise from extra-cellular, non-pathogenic, 

 symbiotic microorganisms. There was nothing to indicate 

 that they had not developed from the mitochondria nor- 

 mally present in the cells of the explanted tissues. It was 

 also presumed that these symbiotic microorganisms were 

 acquired by the animal after birth. Hence, to avoid this 

 uncertainty, it was deemed advisable to choose for experi- 

 mentation those tissues in which the possibility of con- 

 tamination would be reduced to the minimum. 



The tissues of the fetus and the new-born, at least theo- 

 retically, should be uncontaminated by extraneous micro- 

 organism.s and consequently were chosen for the proposed 

 culture experiments. 



The problem of a proper culture mediiun offered, perhaps, 

 the greatest difficulty. It appeared that it would be neces- 

 sary to use a medium which possessed the essential at- 

 tributes of cytoplasm, inasmuch as mitochondria normally 

 live in a cytoplasmic environment. This idea suggested the 

 use of some kind of hving protoplasm as a culture medium, 

 but on further reflection it was obvious that any positive 

 growth in such a medium, would not furnish conclusive 

 evidence on the point at issue. At best, it would permit 

 of various interpretations which would only lead back 



