128 PHYSIOLOGY OF YEASTS (Continued) 



process of its formation. They form a little mass at one of the poles 

 made up of a few cells. This mass is soon surrounded by a number of 

 cells resulting from the segmentation of the reproductive vesicles 

 and of blastodermic origin. This polar mass remains distinct from all 

 of the other organs during the development of the embryo. It is 

 placed in the rear part of the abdomen of the growing cells, the yeasts 

 penetrating into their interior until the mass parts into two bodies 

 which take positions on both sides of the intestines as described above. 



Sulc and Pierantoni have been then led to conclude that the 

 pseudo-vitellius, green body or oval body constitutes organs resulting 

 from a sort of inflammation produced by these yeasts on the blasto- 

 dermic cells in the course of segmentation. Sulc has designated them 

 as mycetomes, reserving the name mycetocytes for the same cells filled 

 with yeasts. 



Both of these investigators admit that the yeast found in the 

 mycetomes is living in symbiotic relation with the insect. At first 

 the yeast was probably a parasite but a continued association with the 

 insect brought about a symbiotic association. According to Sulc the 

 mycetomes play a similar role to that of the lymphatic ganglions. 

 They protect the insect from the invasion of bacteria, by means of 

 the yeasts which are contained in their interiors, for it has been shown 

 by the investigations of Haydruck and Fernbach that they are germi- 

 cidal. On the contrary, Pierantoni x believes that the mycetomes play 

 a role in digestion. The homoptera live on vegetable sap and take in 

 much starch and sugar. Part of these hydrocarbons is assimilated, 

 the rest remaining in the intestinal tract to be finally eliminated. This 

 author thinks that the yeasts in the mycetomes serve in the assimila- 

 tion of the carbohydrates and in the transformation to carbon diox- 

 ide and alcohol. This question apparently needs further study. 



Vandevelde 2 has paid considerable attention to the question of 

 symbiosis in yeast. He has carried rather extensive investigations. 

 When certain yeasts fermented together, the fermentation was car-* 

 ried on to a further degree. The conclusions which this author draws 

 from his investigations are that mixed yeasts give better results than 

 pure cultures in the fermentation industries. It is interesting to 



1 Pierantoni, U. L'origin di alcuni organi d'Icerza perchasi e la simbiosi 

 eredaria. Bull. Soc. Napoli, 23, 1909; Origine e struttura del corpo ovale 

 del Bactylopius citri e del corpo verde dell' Aphis brassicae. Ibid. 24, 1910. 

 Ulteriori osservazioni sulla simbiosiereditaria degli omotteri. Zool. Auz. 36, 

 1910. 



2 Vandevelde, A. J. J. Chemical phenomena in the symbiosis of yeasts. 

 Rev. Gen. Chim. 18 (1915), 88-95; On symbiotic life of yeast races. Original 

 Communications, 8th International Congress of Applied Chemistry, 14 (1912) 

 191-202. 



