Section IV, 1918 [203] Trans. R.S.C. 



A Rosette Forming Organism 

 By F. C. Harrison, D.Sc, F.R.S.C. 



(Read May Meeting, 1918) 



This organism was found in a sample of ropy or slimy milk, its 

 presence being discovered when making a microscopic examination 

 of the affected milk, and it was subsequently isolated by successive 

 platings. 



The organism is peculiar owing to its forming rosette-shaped 

 masses. Singly, it is slightly curved, resembling the bent rods of the 

 tubercle bacillus, but usually somewhat thicker; it is Gram positive, 

 grows well on ordinary media, has an optimum temperature of 

 25°-27°C., thermal death point of 63°C. for ten minutes, and gives a 

 peculiar and characteristic odour to milk, whey and other liquids. 



The peculiar interest of this organism is not, however, in its 

 cultural features but in the formation of the rosettes, or clusters of the 

 bacillus, all the rods radiating from a common centre forming a whorl 

 which may be compared to the petals of a daisy. The number of 

 individuals in a rosette or cluster varies from two or three to fifty or 

 sixty, or more, appearing when examined in hanging drop as a burr, 

 but when on the slide giving a daisy or aster-like appearance. The 

 rosettes are formed on both solid and liquid media. Involution forms 

 in old cultures are frequent, and' the changes in shape vary, — short 

 stunted rods, crescent shape with the middle thicker than the ends, 

 lemon shape, club shape, and occasionally threads; in fact, the 

 diversity in shape was so marked that at first it was thought that other 

 organisms were present, but this idea was found incorrect. 



The formation of the clusters was observed under the microscope 

 in hanging drops in Bottcher's cells, and whilst there was considerable 

 difficulty in observing the development of a single organism owing to 

 its motility, the process could be followed fairly well. 



An organism lengthens and divides and then seems to swing apart 

 until an acute angle forms. This is a gradual movement, and not the 

 so-called "snapping" movement described by Hill. These two 

 organisms again divide and the swing apart again takes place from the 

 ends in contact; if both divide at the same time a rosette of four cells 

 results. Often one rod divides before the other, and a three-rayed 

 cluster forms. When this operation goes on for some time a large 

 rosette is the result. Two organisms lying close to one another will 



