188 



INFECTIVE DISEASES. 



on the solution for ten minutes to half an hour, then trai.sfer them 

 to iodine-potassic-iodide solution, until they assume the colour of a 

 tea leaf ; then immerse them in alcohol until they are decolorised ; 

 dip them in an alcoholic solution of eosin for a few moments, and 

 then transfer them to clove oil to clarify the film ; to remove the 

 clove oil gently press the cover between two layers of clean filter 

 paper, then mount in xylol balsam. 



A good method for cultivating streptococci is to employ a steril- 

 ised looped platinum wire, and to spread a droplet, for example, of 

 pus or blood, over the surface of nutrient agar-agar solidified obliquely. 



a - '> c. 



FIG. 90. STREPTOCOCCUS PYOGENES Bovis. Pure-cultures on nutrient 



gelatine. 



a, Sub-culture from agar. b, Sub-culture from broth. 



c, Sub-culture from milk. d, Sub-culture from milk. 



The tubes are then placed in the incubator at 37 C. ; the strepto- 

 cocci will appear in the course of two or three days in the form 

 of minute dotted colonies. If present alone, and in considerable 

 quantities, the inoculated surface will exhibit a pure cultivation 

 consisting of a number of such colonies, whilst a flocculent mass is 

 observed in the liquid which collects at the bottom of agar-agar 

 tubes ; this flocculent mass will be found to be composed of chains. 

 From such a tube inoculate a number of the small flasks employed 

 in Pasteur's laboratory for cultivations in liquids. In this way 

 a number of pure- cultivations in milk and broth are established, 

 which can le readily examined from time to time. From a pure- 



