VACCINE-THERAPY 17 



Method. — Expose the carotid of a horse with due anti- 

 septic precautions, and insert a sterile cannula into the 

 vessel. The blood should now be collected in a sterile jar 

 by means of a rubber tube fixed to the end of the cannula, 

 and allowed to clot for twenty-four hours. 



The serum is then drawn off with sterile pipettes, placed 

 in sterile test-tubes, and solidified by heating to 70° C, 

 the tubes, of course, laid on their sides at a proper angle to 

 give the necessary slope. 



Potato. 



Method. — The skin should be well scrubbed and peeled 

 sufficiently deep to remove the eyes; cut into long fingers, 

 and round the ends. Now divide into two, cutting obliquely, 

 so that when one is inserted in a test-tube it will have the 



W^^awiMimmu! 



Fig. 8. — (^i) Potato Finger. {B) Cut diagonally ready for 



Insertion in Tube. 



shape of a sloped gelatin or agar medium (Fig. 8). Soak 

 well in cold water for twelve hours, put each into a test- 

 tube, plug, and sterilize for three-quarters of an hour on 

 three successive days. 



Filling and Preparing Test-Tubes for Cultivation. 



Having prepared the medium, we require sloped and 

 stabbed test-tubes ready for use. Each tube should be 

 plugged with cotton-wool, and a number thus prepared 

 laid out on the table. A piece of glass tubing should 

 be procured, on one end of which a rubber pipe 

 should be fixed, the glass tubing having been previously 

 marked to allow the taking up of a given quantity of 

 medium each time. The glass end should now be inserted 



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