Methods of Determination of Pathogenic Microbes. 107 



small in order that the dried preparations may form 

 a very thin coating, which, after staining, will not 

 obstruct the passage of the rays of light. This 

 recommendation is of special importance in the case 

 of organic fluids containing many histological ele- 

 ments, such as pus, for example, of which only a very 

 small particle should be taken. 



Before all staining, it is sometimes necessary to re- 

 move the fatty matters from the dried substance by 

 immersing it in chloroform or a mixture of equal 

 parts of alcohol and ether; this practice is indispensa- 

 ble in operating upon milk. 



Preparations of dried blood are also much im- 

 proved by this treatment : under the influence of the 

 alcohol and ether mixture the corpuscles acquire a 

 stability which desiccation can not confer upon them, 

 and they then present very distinct forms in stained 

 preparations, in which their relations with the mi- 

 crobes can be studied. This is a highly commenda- 

 ble practice which much increases the precision of 

 researches bearing upon the blood. It should be fol- 

 lowed by a second drying. 



Organic pulps. — These are obtained by scraping the 

 freshly cut surface of the organ suspected of contain- 

 ing microbes ; a small particle is spread out between 

 two cover glasses in a thin layer, in the manner indi- 

 cated above, and then dried. 



Microscopic sections. — Tissues which are intended to 

 be cut for the study of the distribution of the mi- 

 crobes which may be present, should, first of all, be 

 well fixed, that is, their elements well immobilized as 

 regards their form and relations, and thus placed be- 

 yond the reach of cadaveric changes. This is es- 



