492 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS portional to the partial volumes. Such an analysis is carried out either with an integrating stage, a point-counting device, or a photomicrograph. Phase contrast techniques can also be used in reflected light. It is then necessary that the specimen surface be relatively smooth and not give too diffuse a reflection. The sensitivity for detection of relief, or optic path difference in general, is higher in reflected light than in transmitted light. The sensitivity for detection of surface relief is approximately four times higher in incident than in transmitted light phase contrast. In incident or reflected light the path difference enters twice. This causes a gain of a factor of 2 in sensitivity. In transmitted light, one would have to examine a replica of the same relief. With a replica refractive index of 1.5, the ef- fective path difference against air would only be 1.5 - 1.0 = 0.5 of the 700 660 560 460 rn,a Figure 4.--Reflection spectra of human hair. bl =- bleached hair dr = titian red lr = light red bd = blond dbd = dark blond bk = black wp = white paper surface.

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).