244 MANUAL OF MICROBIOLOGICAL METHODS 



to remove brain tissue, and the technique of this procedure is relatively 

 simple. The skin over the skull is dissected and reflected back, the sur- 

 face of the skull is disinfected as before, and with an appropriate pair of 

 small sharp scissors a series of small cuts is made around the temporal 

 and occipital edges of the skull. The skull cap can then be removed. In 

 the case of large animals, such as monkeys, cats, or dogs, it may be neces- 

 sary to use bone forceps for this purpose. After the roof of the skull has 

 been removed and the larger cranial nerves cut, the entire brain is lifted 

 out and placed in a sterile petri dish. Upon completion of the autopsy 

 the animal should be carefully placed in a paper bag or similar container 

 and the carcass either sterilized or incinerated; the latter procedure is 

 preferable. Instruments, etc., are sterilized and then washed and dried. 



In an ordinary standardized autopsy it is customary to remove portions 

 of the liver, spleen, kidney, lungs, and occasionally the lymph nodes; 

 other tissues, such as brain and heart, or exudates are taken as indicated. 

 Small portions of the tissues, removed with sterile instruments, may be 

 dropped into tubes of culture media or rolled across the surface of solid 

 media in plates. 



A simple and often profitable procedure is the preparation of impression 

 film.s from tissues. It is sometimes possible to save a considerable 

 amount of time by an examination of impression films prepared immedi- 

 ately after autopsy. The proper manner of preparing films is to lift a 

 small piece of the tissue with a pair of sterilized forceps and carefully blot 

 the cut surface on sterile gauze. It is then momentarily pressed, gently 

 but firmly, against the surface of a glass slide which, after fixation and 

 staining, provides an excellent field for detection of bacteria and occa- 

 sionally even typing of the cellular exudate or histopathology. When 

 tissues are to be fixed for sectioning and microscopic examination, por- 

 tions of the tissues can be placed in the fixative at the same time that 

 cultures are prepared. If it is desirable to retain the original tissues, the 

 material should be placed in sterile wide-mouthed bottles fitted with a 

 plastic screw lid, and these can then be further sealed with liquid paraffin 

 at the junction of the bottle and the lid. Material can be either stored in 

 a 4-8°C refrigerator or frozen, depending upon the conditions. 



THE DETECTION OF ANTIGEN IN TISSUES 



In contrast to the virus diseases it is not usually necessary to resort to 

 antigenic extraction from tissues for making a definitive diagnosis. It is 

 simpler and more reUable to demonstrate microorganisms in infected 

 tissues by cultural methods or by direct microscopic examination. How- 

 ever, in recent years, certain procedures have been developed whereby 

 extraction of infected tissue and subsequent use of the extract as an 



