TEXT-BOOK OF BACTERIOLOGY. 151 



Third, a specific micro-organism must occur in such quanti- 

 ties and so distributed within the tissues that all the symptoms of 

 the disease may be clearly attributable to it. On this point also 

 the peculiar manner in which, under certain circumstances, the 

 bacteria produce their effects demands careful attention. The an- 

 swer to the question whether a particular bacterium fulfils these 

 conditions or not is afforded by microscopic examination. 



This is conducted according to ordinary well-known rules and 

 requires no special explanation. 



The results obtained with the microscope are efficiently aided 

 and protected by the collateral use of artificial breeding. Here we 

 often find an obstacle in the fact that our artificial food media, as 

 we know, do not offer a suitable habitat for all species of bacteria. 

 Yet many an apparently insuperable impediment may be removed. 



Such was the case with the tubercle bacilli in breeding which 

 Koch achieved a brilliant success, though perhaps such ingenuity 

 and acuteness as his may rarely be met with. In many cases the 

 culture to be successful must be conducted throughout with all 

 imaginable precautions. The following illustrates this : Given a 

 rabbit which has, within a few hours, died of a disease the nature 

 of which, let us suppose, we are as yet in ignorance of. By making 

 simple cover-glass preparations of the blood or tissue fluids, it may 

 at once be seen that bacteria are very probably ponnected with the 

 death of the animal. Supposing these bacteria present in the form 

 of short rods, our next task is to develop these suspicious-looking 

 forms artificially, in order to learn further details regarding them. 

 As it is, of course, very important to keep the original material 

 free from pollution by foreign matter, the greatest care should be 

 taken during the following procedure. 



The body of the animal is laid on its back and fastened to a 

 board, the pelt being washed with -fafi solution of sublimate, to free 

 it from all dirt, before an incision is made. We must sterilize be- 

 forehand, in a flame, a number of knives, scissors, and forceps, and 

 place them under a bell-glass for protection. Now take the scis- 

 sors, cut open the skin along the median line, without injuring the 

 abdominal walls, and push it as far back as possible on either side 

 i.e., skin the animal as far as necessary. 



Fresh instruments are then taken in order to avoid pollution by 

 stray germs. The abdominal walls are cut through, and now, with 

 fresh instruments as often as possible, the organs of the abdomen 

 are taken out, and after the breast-bone has been removed, those 

 also of the thoracic cavity. Each organ is placed in a sterilized 

 glass dish. The order usually observed in removing the organs is 



