280 



LABORATORY EXERCISES IN BACTERIOLOGY. 



the pipette by blowing into the upper end, which is plugged with a sterile cotton stopper, 

 and from the bulb by the application of heat. The syringe and all its parts should 

 have been sterilized by boiling or in the autoclave, or by prolonged immersion in a 

 disinfecting solution, with subsequent rinsing in sterile water. The fluid in w r hich 

 the bacteria are suspended having been drawn into the syringe, a fold of the skin is 

 pinched up with the fingers or a pair of forceps and the needle is thrust into the sub- 

 cutaneous tissues of the fold, penetrating some distance from the point of entrance. 

 The fluid is then forced gently and steadily into the tissues and the needle then with- 

 drawn. It is usually unnecessary to do anything more ; but if desired, a drop of collodion 

 may be applied to the point of puncture. 



FIG. 68. DIFFERENT FORMS OF ANIMAL HOLDERS. 



In introducing a solid culture under the skin, after having cleansed the surface 

 as in the previous description, it is necessary to cut with a sterile scissors a small fold 

 of the skin pinched up by the fingers and then holding the edge of the incision with 

 a sterile forceps to break a small pocket with any convenient sterile instrument in the 

 subcutaneous tissues, into which the culture is carried on a stout platinum needle ; 

 the skin wound is then closed with a collodion dressing. 



It is impossible, without some previous knowledge as to the degree of virulence 

 of a bacterium, to determine precisely the dosage of the material to be inoculated into 

 an animal; however, as a general rule for subcutaneous injections it is customary to 

 employ about one per cent, of the body weight of the experiment animal of an active 

 bouillon culture. 



Intravenous Inoculation. This is generally performed on rabbits, the vein 

 along the posterior border of the ear of this animal being an easy one for entrance 



