170 IDENTIFICATION OF BACTERIA 



tetanus and diphtheria antitoxins, varying proportions of antitoxin- 

 toxin mixtures must be injected into guinea-pigs. It will thus be 

 seen that numerous circumstances arise in practical bacteriology 

 when the animal experiment is absolutely necessary and unavoidable. 

 Animal inoculations are also necessary in the preparation of anti- 

 toxins, of antirabic virus, in the immunization against Texas fever, 

 rinderpest, etc. 



In conducting experiments on animals it is generally necessary first 

 to restrain them. Numerous operating tables, both large and small, 

 with restraining devices and holders for mice and guinea-pigs and 

 larger animals, have been constructed. Generally elaborate devices 

 are unnecessary, and a few boards of varying sizes with four nails 

 or blocks driven into the corners will suffice. To the latter the 

 outstretched legs of the animal are fastened with twine. The prin- 

 cipal instruments used in inoculation experiments are hypodermic 

 syringes; however, operating knives, scissors, forceps, needles, suturing 

 material, and even trephines may be needed in certain procedures. 

 The most important factor in all animal experiments is the necessity 

 of strictest asepsis, in order that accidental and misleading results may 

 not be obtained. Injection of a bacterial culture, pathogenic excretion, 

 blood, milk, etc., into an animal requires shaving and thorough anti- 

 septic cleansing of the part to be inoculated. The inoculation is 

 made with a sterile syringe, and the operator must work with clean, 

 antiseptically treated hands. 



Subcutaneous Inoculation. Subcutaneous inoculation is one of the 

 most common methods practised. In its simplest form it consists of 

 a slight incision in the skin without any aseptic precautions, followed 

 by rubbing a little of the suspected material into the wound. This 

 method is sufficient for the experimental identification of anthrax or 

 bubonic plague bacilli. In other instances a deep pocket must be made 

 by pushing a probe under the skin through a small incision and 

 lifting up the skin, forming thus a deep protected pocket. This 

 method is used for inoculating material suspected of containing 

 tetanus bacilli or spores. 



When the subcutaneous method is used with asepsis the skin must 

 be shaved and cleansed and a sterile hypodermic needle employed. 

 In using hypodermic syringes the operator must be careful not to 

 contaminate himself with the dangerous bacteria which he may be 

 handling. A good syringe with a tightly closing piston should be 

 used. Immediately after the injection the entire instrument, including 

 the needle, should be placed in a vessel with water that is slightly 

 alkaline and boiled. The operator must then thoroughly cleanse his 

 hands in a strong bichloride solution. 



Intravenous Inoculation. Another method of inoculation frequently 

 used is the intravenous injection in which the material is injected 

 directly into a vein. In most animals the jugular can generally be 

 used for this purpose. The skin over it is shaved and cleansed anti- 



