V] METHODS OF INOCULATION 6i 



permanent plate-cultivations on gelatine or Agar, and which 

 I first described in the Reports of the Medical Officer of the 

 Local Government Board for 1886-1887, is the test-tube 

 plate-cultivation. It is this : in ordinary plate-cultivations 

 such as were described above it is obvious that only a 

 certain proportion of the colonies appearing on subsequent 

 incubation are situated on the surface, another proportion are 

 in the depth, and these latter are either not characteristic 

 for differential purposes or cannot easily be used for further 

 operations. It is therefore advantageous to have all colonies 

 appearing on the surface. This can be done in two ways : 

 {a) By pouring out into the plate-dish the gelatine or Agar 

 before inoculation, letting it set, and then smear or rub 

 over the surface of the set gelatine or Agar by means of 

 the platinum loop the infective material (see Fig. 12), 

 or (b) by rubbing it over the surface of gelatine or Agar, 

 set with slanting surface in test-tubes. In both cases all 

 colonies make their appearance on the surface only. The 

 latter method allows of the test-tube plate-cultivation to be 

 preserved uncontaminated, as the test-tube on opening for 

 the object of making subcultures can be held mouth down- 

 wards and safe against accidental contamination. When we 

 are dealing with microbes liquefying gelatine the test-tube 

 cultivations in gelatine are not practicable. The test-tube 

 gelatine-cultivations yield excellent impression-preparations 

 (see Chapter I.) ; for this purpose the interior of the test- 

 tube can be easily cast out on to a glass plate by dipping 

 the lower part of the test-tube for a few seconds in hot 

 water ; too long exposure would melt the gelatine and spoil 

 the gelatine block for further operations. 



2. Inoculations with Blood, Juices, and Tissues. — To 

 establish a cultivation from blood of a dead animal, cut open 

 the thorax by removing the sternum with clean scissors, cut 



