74 THE BACTERIOLOGICAL EXAMINATION OF MILK 



the superfluous fluid, and with a sterilised needle or pipette take 

 up a small quantity of the sediment remaining in the tube. 

 Spread the sediment evenly over the surface of an ordinary glass 

 slide and dry over the flame of a Bunsen burner or on the drying 

 stage. Wash the fixed film with ether (or alternately with absolute 

 alcohol and ether) until all the superfluous fat is removed, and 

 stain. The preparation may be stained {a) by one of the 

 ordinary solutions, such as Loffler's blue, etc. ; or {b) by Gram's 

 method. Examine under the microscope with a yV^h oil immer- 

 sion lens. 



Inoculation of animals — 



For details respecting the inoculation of animals, books dealing 

 more especially with general technique may be consulted. Here 

 it will be sufficient to remark that the simplest forms of inoculation^ 

 are all that are usually required in milk investigation, namely, 

 the intraperitoneal and the subcutaneous. In some cases it may be j| 

 sufficient to inoculate a few c.c. of the original milk ; but, as a " 

 rule, it is advisable to centrifugalise, or use the sedimentation 

 flask containing about 250 c.c. From the deposit or sediment 

 two guinea-pigs may be inoculated, the one subcutaneously inj 

 the groin, the other intraperitoneally. Particularly is this necessar) 

 in making a reliable and exhaustive search for the B. tuberculosis^ 

 Microscopic examination alone for this organism is not reliable 

 {see p. 70). The details of the process as carried out in practice 

 are as follows : — 



After centrifugalisation the deposit is mixed with the 2 c.i 

 of milk remaining in the tube after aspiration of that which is 

 superfluous. Two guinea-pigs (of say 250 grammes weight each] 

 are taken and inoculated with the deposit from about 40 c.( 

 of milk. The fluid is inoculated subcutaneously on the inner side 

 of the leg under strict aseptic precautions (the skin having beet 

 washed with i-iocx) corrosive sublimate, and shaved). In less thai 

 a fortnight's time, if the inoculated milk contained a considerable 

 number of tubercle bacilli, typical infection of the popliteal and 

 inguinal glands can be detected. If the milk contained very few 

 bacilli the infection is much slower (fifth week). After the animal 

 has been killed the presence of the tubercle bacilli can be detected 

 in the inguinal glands and the spleen. Some workers make it a 

 rule to inoculate two guinea-pigs from the sediment of the milk, 

 one receiving half of the sediment subcutaneously in the groin, the 

 other receiving the remaining half intraperitoneally. 



