NUTRIENT MEDIA AND METHODS OF CULTIVATION. 113 



sown upon the gelatine which has been already altered by the 

 growth of another micro-organism; the change produced in the 

 jiflatine, as in the case of the Bacillus pyocyaneus, extending far 

 beyond the limits of the growth itself. 



Nutrient jelly may also be spread out on sterilised glass slides, 

 which after inoculation are placed in damp chambers for the growths 

 to develop. 



Esmarch's Roll-cultures. Esmarch introduced a modification 

 of the method of plate- cultivation which may sometimes be used with 

 advantage. The ordinary test-tubes may be employed, or tubes 

 considerably larger in size. 



After the liquid jelly has been inoculated in the tube, instead 

 of pouring it out on to a glass plate or into a dish, the cotton- wool 

 plug is replaced, and an india-rubber cap fitted over the mouth of 

 the tube. 



The tube is then placed horizontally on a block of ice or 

 in a vessel containing iced water. The neck of the tube is steadied 

 with the left hand, and the tube turned round and round with the 

 right hand. In a very short time the gelatine sets, and the tube 

 is lined inside with a thin coating. There is far less danger of 

 contamination, and the cultures are in a much more convenient 

 form when circumstances render it necessary to move them. 



(c) PREPARATION AND EMPLOYMENT OF SOLIDIFIED BLOOD SERUM. 



Solid Blood Serum. The tubercle-bacillus, the bacilli of 

 glanders and of diphtheria, and many other micro-organisms, thrive 

 well when cultivated on solid blood serum. This medium has' the 

 additional advantage of remaining solid at all temperatures. The 

 technique required for its preparation and sterilisation is as follows : 

 Several cylindrical vessels, about 20 cm. high, are thoroughly washed 

 with carbolic acid (1 in 20), and then with alcohol, and finally 

 rinsed out with ether. The ether is allowed to evaporate, and the 

 vessels are then ready for use. The skin of the animal selected 

 calf, sheep, or horse is washed with carbolic at the seat of operation, 

 and the bleeding performed with a sterilised knife or a trocar and 

 rannula. The first jet of blood from the vein is rejected, and that 

 which follows is allowed to flow into the vessels until they are almost 

 full. The ground-glass stoppers, greased with vaseline, are replaced, 

 and the vessels set aside in ice, as quickly as possible, for from 

 t \\vnty-f our to thirty hours. By that time the separation of the 

 clot is completed, and the clear serum can then be transferred to 



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