CULTURAL TECHNIQUE 33 



transmitted and reflected light. Specific or technical terms are 

 used to describe these characters. These the student should 

 learn at an early date, so as to acquire habits of precision in 

 the matter of species description. In the examination of deep 

 colonies, i.e. imbedded in the medium, note the form, size, 

 microscopic structure, consistency, color, change in surround- 

 ing medium. Deep colonies as a rule are far less character- 

 istic than the superficial ones. 



Test-tube cultures. The pure cultures are maintained and 

 are studied in " tube cultures." The transfers are made by 

 means of the platinum needles from the colony on the plate 

 culture to tubes containing various kinds of media. A large 

 part of the detailed study of an organism consists in noting 

 the character of the growth and the changes produced in 

 various media in the absence of all other forms, i.e. in pure 

 culture, by the organism in question. 



Fishing. In the preparation of test-tube cultures from the 

 plate cultures care should be taken in the selection of the 

 colony from which the tube culture is to be inoculated. 

 The plate should be examined macroscopically and a ring 

 drawn with a colored wax pencil about each colony to be 

 used. The colony and its immediate neighborhood should 

 then be examined under the low power of the microscope, 

 in order to determine whether there are any near-by micro- 

 scopic colonies. Mark the colonies which show a clear zone 

 of several millimeters in width about them. Sterilize the 

 platinum needle, remove the cover of the Petri dish, and 

 touch the colony with the end of the needle. With the in- 

 fected needle inoculate the test-tube culture ; mere contact 

 of the inoculating needle with the surface of the colony is 

 amply sufficient to obtain cells enough to seed the new cul- 

 ture. It is not necessary to transfer a visible amount of 



