THE MICROSCOPE IN DIAGNOSIS. 315 



the white blood-cells (see pages 189 and 309). They 

 are easity seen by the microscope in a drop of purulent 

 matter placed on a slide and covered by thin glass. Pus- 

 corpuscles shrink in size on being placed in liquid of 

 greater specific gravity than serum, and are destroyed by 

 the action of caustic alkalies so as to be changed into a 

 tenacious glairy mass. Dilute acetic acid causes them to 

 swell and become transparent, exhibiting from one to four 

 nuclei. Bacteria and their germs (microzyrnes) are often 

 seen with pus, and indicate commencing decomposition. 



According to Dr. Beale, the figures and descriptions 

 generally given of pus represent dead, not living pus. He 

 recommends a little pus to be taken from suppurating 

 skin or mucous membrane and examined at once, in order 

 to see the projections from the bioplasts, by the detach- 

 ment of which they multiply. He considers the " mucous 

 corpuscle" to be nothing more than an imperfect epithe- 

 lial cell surrounded by the viscid mucus formed by it. 

 This may grow rapidly, and the resulting particles become 

 true pus-corpuscles. 



Richardson regards the difference between pus and 

 mucus to be that "the liquor muci is a secretion, which, 

 having been acted upon by the germinal matter of the 

 epithelial cells covering the basement mucous membrane, 

 is not albuminous, while the liquor puris is an exudation, 

 which contains albumen, that may be recognized by ap- 

 propriate tests." 



IV. EXAMINATION OF MILK. 



Examination of human milk may sometimes aid in 

 diagnosis, as in contusions of the breast, incipient mastitis, 

 and in the diarrhoea and innutrition of infants. The origin 

 of milk may be elucidated by the remarks on lactification 

 on page 233. 



A thin stratum of milk should be examined with a 

 power of from 200 to 400 diameters, and an estimate 



