94 CLINICAL BACTERIOLOGY. 



If it is desired to make plates of agar-agar, special pre- 

 cautions must be observed in consequence of the ready 

 coagulability of this culture-medium (even at 39 C. 

 102.2 F.). After the agar has been liquefied, best in boil- 

 ing water (it melts at 90 C. 194 F.), the tubes are placed 

 in a water-bath at a temperature of 40 C. (104 F.). At 

 this temperature the agar just remains liquid, and the bac- 

 teria can be inoculated without suffering in vital activity. 

 The pouring of the agar in the double dishes is unattended 

 with difficulty, as is likewise the preparation of dilutions 

 according to the same method ; only it is necessary to be 

 expeditious in the execution of the manipulations in order 

 to avoid solidification of the agar in the tubes. 



The use of the gelatin-tube itself as a plate is rendered 

 possible by Esmarcti s modification of the Koch procedure : 

 The liquefied tubes, which are best closed with a plug of 

 nonabsorbent cotton not freed from fat, in order to avoid 



Fig. 25. Esmarch's roll-culture : a, India-rubber cap ; b, 6, b, longitudinal line 

 drawn on the tube ; c, c, c, transverse lines for counting colonies (Frankland). 



saturation with the fluid, are inoculated, closed with a rub- 

 ber cap, held in ice-water, and rapidly and regularly rotated 

 about its axis. The gelatin is, by this means, distributed 

 in a thin, even layer on the inner surface of the tube, is 

 solidified, and in this way a roll-plate (Fig. 25) is prepared, 

 which is then further treated in the same way as ordinaiy 

 plates. 



To prepare so-called agar streak-plates for rapid diagnosis, 

 the liquefied agar is poured out before inoculation. When 

 it has solidified, six or seven strokes are made side by side 

 upon an agar-plate with a platinum needle that has been 

 dipped in the fluid to be examined, or with the material to 

 be examined itself (membrane, cotton swab, etc.). Upon 

 the last stroke the bacteria will be so sparsely distributed 

 that individual colonies develop. According to the same 

 principle of dilution, the surface of a number of agar or 

 blood-serum tubes solidified in a slanting position is 



