POST-MORTEM EXAMINATION OF INFECTED ANIMALS. 281 



appear larger than usual, and really beautiful specimens 

 may be obtained. 



In anthrax and other diseases the specific organisms are present- 

 in large numbers in the blood, and tend to accumulate in the narrow 

 capillaries. Thin sections of the internal organs and other tissues, 

 on staining, will reveal the presence of these bacteria. Sometimes 

 beautiful demonstrations of the crowding of bacteria into the capil- 

 laries can be obtained by making preparations of the mesentery. 

 For this purpose a large animal, rabbit or guinea-pig, is desirable. 

 A portion of the intestine should be stretched so as to expose the 

 mesentery. A cover-glass is dropped on the clean mesentery, and 

 the intestine is then laid over the glass-slip. With a pair of broad- 

 pointed forceps the cover-glass is firmly seized and turned over so 

 that the membrane covers the entire upper surface. The mesentery 

 is then cut loose with a pair of sharp scissors. The cover-glass now 

 is covered on one side by a thin piece of the mesentery. It is placed 

 in an Esmarch dish and covered with absolute alcohol, to which a few 

 drops of formaldehyde are added. The specimen is thus fixed in a few 

 hours, after which it is washed with water and stained by Gram's 

 method, if this can be used. The minute branching capillaries will 

 often be found plugged full of bacteria. Appearances of this kind 

 gave rise, at one time, to the hypothesis that bacteria produced dis- 

 ease by mechanical interference with the circulation. 



The cover-glass preparations made from the animal 

 body, in the manner indicated, contain a relatively large 

 amount of organic matter. Consequently, care must be 

 taken to prevent over-staining of the -back-ground, inas- 

 much as this will interfere with a satisfactory examination 

 of the bacteria that may be present. The following proce- 

 dure will enable one to deeply stain the bacteria, without 

 scarcely coloring the back-ground. The importance of this 

 will be recognized when but a few organisms are present 

 on the cover-glass. 



The cover-glass preparation is fixed with a minimum 

 amount of heat. The directions for fixing a specimen have 

 been given on p. 148. 



When the " fixed" glass-slip has cooled, a drop or two 

 of water should be added so as to cover the material. A 



