150 PURE CULTURES FROM PATHOLOGIC MATERIAL 



bacterial growth and the needle is then plunged down vertically into 

 the solid culture medium. This method of inoculating a tube is called 

 a stick or stab culture. It is used when a gelatin tube is inoculated 

 in order to show whether liquefaction takes place or not, and it is 

 also employed in the preparation of anaerobic cultures, because the 

 deeply inoculated bacteria are to a great extent removed from the 

 air in the upper part of the tube. 



Shake Cultures. It is sometimes desirable to distribute the inoculated 

 material evenly in a solid culture medium. The latter is then lique- 

 fied and cooled down to near its point of solidification. The inocu- 

 lation is then made and the still fluid medium, after the closure of 

 the tube with the cotton plug, is shaken violently and finally allowed 

 to solidify in an upright position. Such a shake culture will readily 

 permit the formation of gas bubbles in the developing growth. 



Pure Cultures by Preliminary Animal Inoculations. It is sometimes 

 impossible to obtain the causative pathogenic bacteria in pure culture 

 from a pathologic discharge, excretion, or tissue by direct inoculation 

 of culture media. Even the plate (Petri dish) method is not available 

 in some cases. The cause of tuberculosis, the tubercle bacillus, for 

 instance, grows very slowly, and in tubercular discharge is generally 

 associated with other bacteria. If tubes were inoculated and plates 

 poured from a material of this kind all other bacteria present would 

 develop days before the tubercle bacillus had a chance to form a 

 colony. In a case of this kind it is necessary to inoculate the material 

 into an animal susceptible to tuberculosis. The tubercle bacillus will 

 multiply in its body and be present in certain locations and structures 

 in pure culture. At an appropriate time the animal is killed and under 

 aseptic precautions some of the tubercular material is obtained and 

 brought into the proper culture media to give the tubercle bacillus a 

 chance to develop and form a pure culture. The same method is 

 generally necessary to obtain a pure culture of glanders bacilli from 

 a horse suffering from glanders, because here also the glanderous 

 discharges are contaminated by many bacteria growing more rapidly 

 than the bacillus mallei. Further details about bacteria which have 

 to be obtained in pure cultures in this indirect manner will be given 

 in the chapters devoted to such particular microorganisms. 



Anaerobic Cultures. Anaerobic bacteria which do not develop in the 

 presence of the oxygen of the atmospheric air have to be cultivated 

 under special arrangements which will exclude this gas. Various 

 methods have been developed to accomplish this end. The simplest 

 method, devised by R. Koch, consists in placing a sterile piece of 

 mica over the surface of a plate inoculated with an anaerobic germ. 

 This method was later modified by replacing the mica by a sterile 

 glass plate and sealing the latter around its margins by sterile gelatin 

 or agar to which a small amount of some antiseptic had been added. 

 Methods of this type have been largely abandoned, and have been 

 replacedH)y*betterJdevices. 



