Il8 MICROSCOPIC METHODS. 



scraped off into it. This fiuid is then filtered into the test-glass 

 through a plug of sterile glass wool'. This is easily effected by- 

 taking a piece of | in. glass tubing 3 in. long, drawing one end 

 out to a fairly narrow point, plugging the tube with glass wool 

 above the point where the narrowing commences, and sterilis- 

 ing by heat. By filtering an emulsion through such a pipette, 

 flocculi which might block the needle are removed. If a solid 

 organ or an old culture is used for inoculation it ought to be 

 rubbed up in a sterile porcelain or metal crucible with a little 

 sterile distilled water, by means of a sterile glass rod, and the 

 emulsion filtered as in the last case. 



The methods of inoculation generally used are: (i) by 

 scarification of the skin; (2) by subcutaneous injection; (3) 

 by intraperitoneal injection; (4) by intravenous injection; (5) 

 by injections into special regions, such as the anterior chamber 

 of the eye, the substance of the lung, etc. Of these (2), (3), 

 and (4) are most frequently used. When an anaesthetic is 

 to be administered, this is conveniently done by placing the 

 animal, along with a piece of cotton wool or sponge soaked 

 in chloroform, under a bell-jar or inverted glass beaker of suita- 

 ble size. 



I. Scarification. — A few parallel scratches are made in the 



skin of the abdomen previously cleansed, just sufficiently deep 



to draw blood, and the infective material is rubbed in with a 



platinum eyelet. The disadvantage of this method is that the 



^^,^ inoculation is easily con- 



>A taminated. The method 



I is only occasionally used. 



::^^-^^^;;^ 2. S?tbc?ttaneoiis Injec- 



^■'-^ '^ f^ ' -J^p tion. — A hypodermic syr- 



—- inge is charged with the 



fluid to be inoculated. 



riG. 55. — Apparatus for holding a mouse prepara- Xhe hair is CUt off the 

 tory to subcutaneous inoculation. 



part to be inoculated, and 

 the skin purified with i to lOOO corrosive sublimate. The skin 

 is then pinched up, and, the needle being inserted, the requisite 

 dose is administered. The wound is then sealed with a little 

 collodion. 



3. Intraperitoneal Injection. — This may be performed by 

 means of a special form of needle. The needle is curved, and 



