2l6 PATHOGENIC BACTERIA. 



A special arrangement of the microscope was devised 

 for the purpose, and the number of bacilli in each drop 

 estimated with extreme care. The number varied from 

 472 to 240,000. To estimate the number of bacilli in a 

 given quantity the number of drops to a cubic centimeter 

 is multiplied by the number of bacilli in the drop, and 

 then by the number of cubic centimeters to be estimated. 



The method is an ingenious one, but a glance down 

 the columns of figures in the original article will be 

 sufficient to show that the counting of the bacilli is 

 devoid of any particular value. 



This is only to be expected when one considers the 

 pathology of the disease and remembers that accidents, 

 such as unusually violent cough one day, modified by 

 the use of sedatives the next, may cause wide variations 

 in the quality if not in the quantity of the sputum. 



When the tubercle bacilli are to be sought for in sections 

 of tissue, considerable difficulty is at once encountered, 

 partly because of the thickness of the section and partly 

 because of the presence of nuclei which color intensely. 



Again, Ehrlich's method must be recommended as the 

 most certain and best method of staining a large number 

 of bacilli. 



The sections of tissue, if imbedded in celloidin or par- 

 affin, should be freed from the foreign substances. Like 

 the cover-glasses, they are placed in the stain for twelve 

 to twenty-four hours at a temperature of 37 C. Upon 

 removal they are allowed to lie in water for about ten 

 minutes to wash away the excess of stain and to soften 

 the tissue, which often shrinks and becomes brittle. The 

 washing in nitric acid (20 per cent.) which follows may 

 have to be continued for as long as two minutes. Thor- 

 ough washing in 60 per cent, alcohol follows, after which 

 the sections can be counter-stained, washed, dehydrated 

 in 95 per cent, and absolute alcohol, cleared in xylol, 

 and mounted in Canada balsam. 



A method which has attained great and deserved praise 

 is Unna's. It is as follows : The sections are placed in 



