280 THE PRINCIPLES OF IMMUNOLOGY 



special machines and sealed in capillary tubes. Formerly " ivory " 

 vaccine points were also charged from this pulp, but these have been 

 forbidden in interstate commerce (page 282). In all cases the material 

 before being prepared for distribution is carefully tested for the 

 presence of tetanus bacilli or their spores. Its potency may be deter- 

 mined by directly inoculating the inner surface of the ears of rabbits 

 and observing the rapidity of the reaction. A somewhat superior 

 method is to make dilutions of the virus and to note the effect of these 

 dilutions when inoculated on the ears of rabbits. A potent virus should 

 produce vesicles in a dilution of i to 500. Efforts have been made to 

 secure a virus in purer form and Noguchi has planted the virus in the 

 testicles of rabbits and of bulls. Virus recovered from this situation 

 is not subject to contamination in the same way as that obtained from 

 surface inoculations. The amount of material obtained, however, is 

 small and the method has not been used extensively enough to justify 

 an opinion as to its value. After preparation of a virus the date 

 should be indicated on the container and the material preserved in 

 the ice chest. 



Methods of Inoculation in Man. As a rule, vaccination is applied 

 on the upper arm over the point of insertion of the deltoid muscle. 

 This situation offers protection against injury and contamination such 

 as is not afforded by vaccination upon the leg or thigh. The area is 

 carefully cleansed with soap and water, followed by alcohol or ether 

 and then by distilled water. The last step is sometimes omitted. For- 

 merly the area was scarified in a criss-cross manner by means of a 

 needle or scalpel, but such extensive scarification has been found to 

 be unnecessary and also exposes a greater surface to the possibility 

 of infection. The more modern method is to place the virus upon the 

 area and to make a scarification through the virus. This may be done 

 by a small linear incision, by the drill method or by the multiple punc- 

 ture method. Wright has advised intracutaneous inoculation. 



Method of Linear Incision. Af ter placing the virus upon the skin 

 a sterile needle or a small scalpel is employed for making a scarification 

 through the virus and sufficiently deep into the skin to permit absorption 

 but not to produce bleeding. The virus is then gently rubbed into the 

 abrasion and permitted to dry. If a dressing is desired it should be of 

 sterile gauze loosely applied with adhesive strips after the virus has 

 completely dried. Sealing with collodion should not be attempted, 

 since it may permit more ready growth of contaminating bacteria 

 and produce maceration of the skin. 



The Drill Method. A sterile drill such as is employed in the Von 

 Pirquet cutaneous tuberculin test is held between the thumb and middle 

 finger. With a twisting motion and moderately firm pressure a small 

 abrasion the diameter of the drill is made through the virus. This 

 should penetrate the epiderm, but should draw no blood. 



The Multiple Puncture Method. A sterile needle is held nearly 

 parallel with the skin and the point placed through a drop of virus so as 



