A STUDY OF SPONTANEOUS AGGLUTINATION 83 



salt solution or tap water (the diluents usually employed), they 

 also give spontaneous agglutination. 



Even old stock cultures which fail to give spontaneous agglu- 

 tination at first, will do so, if the culture is inoculated into fresh 

 media or repeatedly sub-cultured on agar, pepton water or 

 broth. Spontaneous agglutination also appears in the suspen- 

 sion of a twenty-four-hour agar culture in water, salt solution, 

 broth, pepton water or diluted senim. 



If we examine an easily changeable stock culture, i. e.,a culture 

 containing both types of colonies, and streak such a culture on 

 the agar plate, we will find the two types of colonies described 

 above. 



If upon plating we can isolate colonies of the non-spontaneously 

 agglutinating type, only occasional sub-cultures from these 

 colonies have to be made for the agglutination test, as such col- 

 onies invariably fail to agglutinate spontaneously, and further 

 tests are unnecessary. 



Agar cultures seem to show greater stability than fluid media 

 cultures; some strains, however, always show one type of col- 

 ony. For example certain strains of Bad. iyphosum which 

 have been handled for a year and a half showed constantly on 

 both solid and fluid media non-spontaneous agglutination. Such 

 a strain is valuable as a stock culture for the Widal test. In 

 many of these cultures, even after being kept for several months 

 in an ice chest, there was only one type of colony present cor- 

 responding with the original form, although some of the cultures 

 were dead. These cultures were made on 0.5 per cent agar 

 medium and the tubes were sealed with paraffin. 



This investigation was made possible by a grant from the 

 National Canners Association, and has been carried on under 

 direction of Prof. M. J. Rosenau of the Department of Preven- 

 tive Medicine and Hygiene, Harvard Medical School, Boston, 

 IMass. 



