152 TEXT-BOOK OF BACTERIOLOGY. 



as follows : First the spleen, then the liver, then the kidneys, next 

 the heart, and lastly the lungs. As a matter of course one is not 

 strictly bound to this order of proceeding 1 ; other organs than those 

 just named will sometimes require attention, and also different 

 species of animals will occasionally require special methods of dis- 

 secting suited to their peculiarities. 



The chief point is never to lose sight of the extreme importance 

 of exactitude and cleanliness. Nevertheless the effects of decom- 

 position, which (in the case of small animals, such as mice) gen- 

 erally begins very soon after death, are apt to interpose and render 

 the determination of the true cause of disease much more difficult. 



When the dissection is completed, proceed to further investi- 

 gations, as follows : Small quantities of blood from different parts, 

 portions of tissue from organs which frequently harbor large quan- 

 tities of bacteria, such as the spleen, the liver, and the lungs, are 

 placed in our liquefied culture media, the usual dilutions are made, 

 and we ascertain, by means of the glass-plate process, whether 

 there are bacteria in this original material, and if so to what spe- 

 cies they belong. 



If the presence of strictly parasitical micro-organisms, which 

 can only thrive at the temperature of the living body, be suspected, 

 we must prepare agar plates and keep them in the incubator. If 

 we have reason to expect anaerobic bacteria, we must adopt suita- 

 ble measures for their examination. 



When the colonies begin to appear the plates are subjected to 

 a close scrutiny. We must find out whether only one kind of bac- 

 teria or a number of different kinds have developed, and in the 

 latter case, whether one kind distinguishes itself by its numerical 

 superiority or by any peculiar qualities. Attention will, of course, 

 be specially directed to such, and we endeavor to find out with the 

 aid of the microscope whether in form and appearance the} 7 are 

 identical with or simulate the bacteria already observed in the 

 cover-glass preparation. 



If we are able to examine many cases in which the disease is 

 apparently one and the same, it becomes much easier to form a 

 judgment based on the indications of the plates, since we may ex- 

 pect that the particular micro-organism will present itself every- 

 where in the same manner. 



If such a bacterium which (firstly) occurs in all cases of the 

 disease in question and (secondly) occurs there in large quantities 

 also presents marked peculiarities of growth or form, enabling us 

 to distinguish it from other species and also to prove (thirdly) 

 that this one definite species is found only and exclusively in con- 



