PRACTICAL BACTERIOLOGY. 



unite to form short threads, which, in an unstained 

 preparation, look like a single rodlet. In older cul- 

 tures, much longer rodlets are seen, which, even 

 when stained, appear to consist of a single cell. On 

 potatoes often somewhat bent rods are formed, es- 

 pecially if the potatoes have an acid reaction and the 

 cultures are old. 



So-called polar granules are found in potato cul- 

 tures, and occasionally in those on other nutrient 

 media. These are collections of protoplasm at the 

 ends of the cells, which become more intensely stained 

 than the remaining plasma. In addition to these 

 granules, there are usually places in which there is no 

 plasma, and which are of course unaffected when the 

 preparation is stained. Formerly it was considered 

 that these granules were spores, but it is more likely 

 that they indicate the commencement of degenei-ation 

 in the cells. At present the formation of spores by 

 these bacilli has not been observed. These granules 

 may pretty certainly be always obtained from very 

 acid or very alkaline potato cultivations, and they 

 may be considered to constitute a reliable specific 

 characteristic, by means of which to distinguish the 

 typhoid bacilli from many other similar organisms. 



Typhoid bacilli are fairly, easily stained although 

 not intensely with any of the usual aniline dyes. In 

 order to obtain a well coloured preparation it is best 

 to use an aqueous solution of gentian violet, .and to 



