254 



Cultures, and their Study 



B 



The Gelatin Puncture Culture. To make satisfactory 

 puncture cultures, the gelatin must be firm and not old and 

 dry. Should the gelatin be soft and semi-fluid at the time 

 the puncture is made, the bacteria diffuse themselves through- 

 out and the typical appearance of the growth may be 

 masked. On the other hand, if the gelatin is old, dry, or 

 retracted, it is very apt to crack after the culture has been 



Fig. 60. Types of growth in stab cultures. A, Non-liquefying: 

 1, Filiform (B. coli) ; 2, beaded (Str. pyogenes) ; 3, echinate (Bact. 

 acidi-lactici) ; 4, villous (Bact. murisepticum) ; 5, arborescent (B. 

 mycoides). B, Liquefying: 6, Crateriform (B. vulgare, 24 hours); 

 7, napiform (B. subtilis, 48 hours) ; 8, infundibuliform (B. prodigiosus) ; 

 9, saccate, (Msp. Finkleri) ; 10, stratiform (Ps. fluorescens) (Frost). 



made and thus entirely destroy the characteristics of the 

 growth. The wire used in the operation should be perfectly 

 straight, and the puncture should be made from the center 

 of the surface directly down to the bottom of the tube and 

 then withdrawn, so that a simple puncture is made. The 

 resulting appearances as the growth progresses are subject 

 to striking variations according to the liquefying or non- 



