The Gelatin Puncture or "Stab" Culture 



209 



gether, it may be necessary to do it under a dissecting microscope 

 or even a low power of the ordinary bacteriologic microscope. 

 This operation of transplantation is familiarly known as fishing. 



Fishing. It requires considerable practice and skill to fish suc- 

 cessfully, and the student should early begin to practise it. The 

 colony to be transplanted, selected because of its isolation, its typical 

 appearance, and convenient position on the plate, is brought to the 

 center of the field and the plate firmly held in position with the left 

 hand. A sterile platinum wire is held in the right hand, the little 

 finger, comfortably fixed upon the stage of the microscope, being used 

 to support the hand. As the operator looks into the microscope the 

 point of the platinum wire is carefully brought into the field of vision 

 without touching either the lens of the microscope or any part of the 

 plate beneath. Of course, the wire and the colony cannot be simul- 



Fig. 58. Microscopic structure of colonies: i, Areolate; 2, grumose; 3, 

 moruloid; 4, clouded; 5, gyrose; 6, marmorated; 7, reticulate, 8, repand; 9, lobate; 

 10, erose; n, auriculate; 12, lacerate; 13, fimbricate; 14, ciliate (Frost). 



taneously focussed upon. When the colony is distinctly seen the 

 platinum wire appears as a shadow, but the endeavor should be to 

 make the end of the shadow which corresponds to the point of the 

 wire appear exactly over the colony. It is then gradually depressed 

 until it touches the colony and can be seen to break up and remove 

 some of its substance; or should the colony be tough and coherent, to 

 tear it away from the culture-medium. It requires almost as much 

 skill to withdraw the wire from the colony without touching anything 

 as to successfully approach the colony in the first place. The 

 bacterial mass adhering to the wire is now spread upon the surface 

 of agar-agar or stabbed in gelatin or stirred in fluid medium, as the 

 case may be. The higher the magnification under which this opera- 

 tion is done, the more difficult it is. Therefore only low-power 

 lenses should be employed. 



The Gelatin Puncture or "Stab" Culture. To make satisfactory 

 puncture cultures, the gelatin must be firm but not old or dry. 

 Should the gelatin be soft and semi-fluid at the time the puncture is 

 made, the bacteria diffuse themselves and the typical appearance 

 of the growth may be masked. On the other hand, if the gelatin be 

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

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