AN HEREDITARY TUMOR 517 



flasks. The culture media which proved most satisfactory was 

 the banana — yeast-agar method, based on the work of several 

 investigators. The formula used w^as that recommended by 

 Baumberger (Science, '17). The media consisted of one cake of 

 yeast dissolved in 50 cc. of water added to one-half dozen mashed 

 bananas, mixing thoroughly and allowing it to ferment for 

 twenty-four hours. This was pressed through a cloth and the 

 resulting liquid heated with 1.5 grams agar-agar per 100 cc. and 

 poured into lErlenmeyer flasks, plugged and sterilized in an 

 Arnold sterilizer three successive days. Thirty sterile eggs were 

 placed in each of four flasks. Larvae with tumors appeared in 

 all the flasks. Larvae from each flask were removed with a 

 sterile platinum loop and placed in plain broth — sugar broth — 

 and allowed to crawl over slant agar. On two of the slant agar 

 and in one dextrose broth I got a pure culture of yeast, but sterile 

 otherwise as regards bacteria. The yeast is necessarily present, 

 since it is the chief food of the larvae. At regular intervals 

 the medium in the Erlenmeyer flasks was tested for its sterility 

 and was in every case found free from bacteria. When the flies 

 emerged from their pupa cases they were passed into other 

 flasks with fresh, sterile media. Some were passed into slant 

 agar tubes and allowed to ,walk over the agar. These tubes 

 were incubated, but no growth occurred except a pure culture 

 of yeast on one agar slant. From the eggs laid by the sterile 

 flies larvae hatched which developed tumors. These larvae 

 were tested for sterility as before and were found free from bac- 

 teria. Since the tumor is developed in larvae bred in absolutely 

 sterile conditions, it is quite evident that it is not due to an 

 infection, taking for granted that an absolutely sterile condition 

 means a condition not only free from the ordinary bacteria of 

 contamination, but also ultramicroscopic organisms. 



It is known that in certain diseases the infection is due to the 

 presence of microorganisms within the eggs, the eggs becoming 

 contaminated from the mother before enclosed in the outer shell. 

 To determine whether the egg is the source of infection in the 

 case of this hereditary tlimor, hundreds of eggs laid upon sterile 

 media by flies free from bacteria were picked and ground up in 



