The Gelatin Puncture or "Stab" Culture 



211 



microscope or even a low power of the ordinary bacteriologic micro- 

 scope. This operation of transplantation is familiarly known as 

 fishing. , 



Fishing. — This is the transfer of a colony from the plate to a 

 fresh medium. It is done by touching the colony with the wire 

 and transferring. When the colony is large and well isolated no 

 particular skill is required, but when many small colonies are closely 

 associated it may be necessary to make the transfer while the colony 

 is under the microscope. A hand lens, a dissecting microscope 

 or the usual bacteriological microscope may be used. In the latter 

 case the low-power objective must be used. The colony to be trans- 

 planted, 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 



Fig. 51.— Microscopic structure of colonies: i, Areolate; 2, grumose; 3, 

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

 10, arose; 11, auriculate; ij, lacerate; 13, fimbricate; 14, ciliate (Frost). 



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

 point of the platinum wire is carefully brought into the field of vis- 

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

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

 simultaneously focused 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 jSkill 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 "vvire is how spread upon the sur- 

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

 the case may be. 



The Puncture or "Stab" Culture. — To make satisfactory punc- 

 ture cultures, the medium must be firm but not old or dry. Gela- 



