EXPERIMENTS UPON THE LIVING ANIMAL. 



135 



Subcutaneous inoculation is very simple and effectual, and con- 

 sequently the method most frequently employed. The animal 

 selected for example, a guinea-pig is held by an assistant, who 

 covers it with a towel, leaving only the hind extremities exposed. 

 By so doing, and gently laying it upon its back, with its head low, 

 a guinea-pig passes apparently into a state of hypnotism, and the 



FIG. 69. KOCH'S SYRINGE. 



trivial operation can be performed with little or no movement on the 

 part of the animal. From a spot on the inner side of the thigh the 

 hair is cut close with a small pair of scissors curved on the flat, and 

 the skin must be thoroughly purified with 1 in 20 carbolic acid. A 

 small fold of skin is then pinched up with a pair of sterilised forceps, 

 and with a pair of sharp sterilised scissors, or with a tenotomy knife, 

 a minute incision is made. A sterilised platinum loop is charged 

 with the material to be inoculated, and the loop is gently inserted 

 under the skin, forming a small pocket in the subcutaneous tissue. 

 The needle is then withdrawn, and the sides of the wound gently 

 pressed into apposition and painted over with collodion. 



FIG. 70. SYRINGE WITH ASBESTOS PLUG. 



In inoculating a mouse the same process is adopted, with the 

 exception that the root of the tail is the usual site of the 

 operation. 



In some cases it may be necessary to inoculate cultures diffused 

 in sterilised salt solution, or blood or lymph containing bacteria, 

 or a culture in broth, or a filtrate containing the toxic products, 



