CULTIVATION BY STROKE AND PUNCTURE. 65 



or less diffuse mass at this spot. Some colonies spread 

 themselves out in concentric layers^ and others in 

 homogeneous masses stretching outwards from the 

 place where the needle entered; some of them are 

 only small in diameter, whilst others spread themselves 

 right up to the sides of the test-tube. Similarly, the 

 ways in which they grow along the puncture line are 

 remarkably different. Frequently a thread is formedj 

 which may be thin and smooth^ or irregular with globu- 

 lar protuberances upon it; sometimes it is thickest 

 above, sometimes below; often fine hair-like processes 

 or thick radiating branches stretch out from the more 

 or less thick stem into the nutrient medium; some- 

 times also a peculiar growth is seen along the track of 

 the wire, no thread being perceived, but only gauzy, 

 cloud-like radiations stretching out from the central 

 axis of the medium. Amongst some micrococci, es- 

 pecially those which act as exciting agents of disease, 

 no coherent thread occurs, but only a row of globules 

 which do not coalesce. 



Further distinguishing characteristics are caused 

 by the fact that some bacteria cause the gelatine to 

 liquefy, and that this may take place in very different 

 ways. Sometimes the liquefaction commences on the 

 surface, gradually and evenly spreading downwards 

 and towards the edge of the vessel; sometimes it 

 occurs simultaneously along the whole length of the 

 puncture, forming a funnel, resembling a sack or a 



