QUANTITATIVE MICROSCOPY 493 '!': •'i"! '? •!i. :" ß .., :• '..- .... : .. ..•::....•:•-•,•--• ß -2. ?,..., * ',•,:• ,•!! .... ':" •. :.-'•....• .• '.: Figure 5.--Interaction between hair washing agent and fat film (phase contrast: 500X). .. ...... .. •,,• -:.-• .....• ?•. '..•. .•. •:...-.½•. • ':,, ,,-. '• .t• '? ..- .:, ..... . ....... ,-..• .... •v:*.•_ • "'% '½ ',..'.'•.•4' ' . '•' • '•"• , :-::2 . '-•-.::: .' % • •. • - . ß '% . -• .%" ?: .. . -' ..,. .½:½%. ., :.. :: g' • ' *' .• •.•:•,•.. .' • •: %. .:• . ... . .. .: •...•... .. .• .. .... , "•. ..., .... .- --7 .: f ,:,.: .•-• {.::..? .. •,- • .2 ? ?-?' .:' 4' ,•. ': . •: ,• -'.... -'-•.' '. ' .. • '.•: .•:. :r •.. .½,•:... ß . _..,. : •. ½%:.,?.: •.(• ..½ :.. .... .... ? ...:.. ...... Figure 6.--Structural features of an emulsion •e oil is distributed in the form of lamellae (phase contrast: 500X).

494 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS . ß '.. / :i• ": '. '"' :: J :" .2.•...:: :/':'7 • .... .•. Figure 7.--Beginning corrosion (reflected light phase contrast: 500X). actual relief depth. This makes reflected light phase contrast more sensi- tive by another factor of 2. The human eye can detect intensity difference of around 5%. With this approximate figure the contrast function leads "7 •.....•'""•,-•'.':'i.-":'"-":'.:".-:" '.".'"".:"7:"'" • '•.' '- .: -.._ '.. =•. 7.•:'&' • : ." :"' . .... g ::. 2 ß ..:. ß : '. •. ... :• .:. •' ...-..:• .... ... .. . . .... . . . . . . .-" '• .7 -' . -:..:•. • ": .& '"!:.. Figure 8.•Surface of human incisor treated with coarse abra- sive (reflected light phase contrast: $00X).