所謂(wei)脫水就是(shi)利用脫水劑將組織(zhi)內的水分置換(huan)出來，以利于(yu)有機溶(rong)劑的滲(shen)入，這一過程稱(cheng)為脫水。

   脫(tuo)(tuo)水(shui)(shui)(shui)是否徹底，直接關系到組織(zhi)是否能(neng)充分(fen)透(tou)明，而脫(tuo)(tuo)水(shui)(shui)(shui)不足或脫(tuo)(tuo)水(shui)(shui)(shui)過度（一般日常工作中這點時間(jian)并不可能(neng)），容易造成組織(zhi)發(fa)脆。造成組織(zhi)發(fa)脆的原因(yin)還有加(jia)溫（溫度超過36℃）、脫(tuo)(tuo)水(shui)(shui)(shui)劑(ji)內加(jia)有丙酮、浸蠟用(yong)的石蠟中二甲苯過多等等。

   一(yi)般我(wo)們總認為組織(zhi)發脆跟高濃(nong)(nong)度(du)(du)(du)(du)酒(jiu)精(jing)(jing)有關，而忽視了與低(di)濃(nong)(nong)度(du)(du)(du)(du)的酒(jiu)精(jing)(jing)關系，其實低(di)濃(nong)(nong)度(du)(du)(du)(du)的酒(jiu)精(jing)(jing)具(ju)有強大的穿透力，比(bi)純酒(jiu)精(jing)(jing)更(geng)容易(yi)滲透到組織(zhi)塊(kuai)內部使之(zhi)脫(tuo)(tuo)水(shui)，組織(zhi)如果(guo)在(zai)低(di)濃(nong)(nong)度(du)(du)(du)(du)酒(jiu)精(jing)(jing)里充(chong)分脫(tuo)(tuo)水(shui)，在(zai)高濃(nong)(nong)度(du)(du)(du)(du)酒(jiu)精(jing)(jing)里只需脫(tuo)(tuo)去從低(di)濃(nong)(nong)度(du)(du)(du)(du)到高濃(nong)(nong)度(du)(du)(du)(du)之(zhi)間(jian)(jian)的水(shui)份，因此，僅(jin)需短時(shi)間(jian)(jian)就可完成(cheng)。

   所謂脫水(shui)(shui)(shui)過(guo)度(du)引(yin)起(qi)組織(zhi)(zhi)發(fa)脆(cui)可能(neng)是起(qi)始(shi)脫水(shui)(shui)(shui)濃度(du)過(guo)高引(yin)起(qi)。如(ru)(ru)果脫水(shui)(shui)(shui)時(shi)(shi)(shi)(shi)加溫(wen)(wen)(wen)(wen)，使(shi)用(yong)丙(bing)酮，還可引(yin)起(qi)組織(zhi)(zhi)收縮(suo)，并影響免(mian)疫組織(zhi)(zhi)化學的(de)(de)標記。為(wei)了使(shi)石蠟(la)浸入到(dao)組織(zhi)(zhi)塊內(nei)，必(bi)須經(jing)過(guo)一(yi)種(zhong)既(ji)能(neng)與(yu)脫水(shui)(shui)(shui)劑(ji)混合(he)，又能(neng)與(yu)石蠟(la)相(xiang)溶的(de)(de)媒(mei)介物質(zhi)，這(zhe)個(ge)過(guo)程稱透明。目前(qian)最好(hao)的(de)(de)透明劑(ji)是二甲(jia)苯。很多人認為(wei)二甲(jia)苯極容(rong)易(yi)使(shi)組織(zhi)(zhi)發(fa)脆(cui)，這(zhe)個(ge)觀點很片面，在常溫(wen)(wen)(wen)(wen)下(xia)，如(ru)(ru)果不(bu)是時(shi)(shi)(shi)(shi)間過(guo)長(chang)（超(chao)過(guo)２4小(xiao)時(shi)(shi)(shi)(shi)以上）二甲(jia)苯并不(bu)會引(yin)起(qi)組織(zhi)(zhi)過(guo)份發(fa)脆(cui)，相(xiang)反(fan)會使(shi)某(mou)些組織(zhi)(zhi)結構比較(jiao)質(zhi)韌的(de)(de)組織(zhi)(zhi)：如(ru)(ru)子宮肌瘤(liu)等相(xiang)當(dang)好(hao)切），但是當(dang)二甲(jia)苯溫(wen)(wen)(wen)(wen)度(du)超(chao)過(guo)36-40℃以后，極易(yi)引(yin)起(qi)組織(zhi)(zhi)發(fa)脆(cui)。脫水(shui)(shui)(shui)時(shi)(shi)(shi)(shi)間（室(shi)溫(wen)(wen)(wen)(wen)18℃）以80％酒精(jing)2小(xiao)時(shi)(shi)(shi)(shi)、95％酒精(jing)（2道）各(ge)1個(ge)半小(xiao)時(shi)(shi)(shi)(shi)至(zhi)2小(xiao)時(shi)(shi)(shi)(shi)、純(chun)酒精(jing)（3道）各(ge)1個(ge)半小(xiao)時(shi)(shi)(shi)(shi)至(zhi)2小(xiao)時(shi)(shi)(shi)(shi)，二甲(jia)苯（2道）各(ge)30-60分鐘為(wei)宜。脫水(shui)(shui)(shui)時(shi)(shi)(shi)(shi)間長(chang)短，與(yu)室(shi)溫(wen)(wen)(wen)(wen)高低(di)有(you)密切的(de)(de)相(xiang)關。我(wo)(wo)們在實踐中發(fa)現(xian)，室(shi)溫(wen)(wen)(wen)(wen)在12～15℃時(shi)(shi)(shi)(shi)，可作為(wei)一(yi)個(ge)臨界溫(wen)(wen)(wen)(wen)度(du)范(fan)圍(wei)(wei)。當(dang)室(shi)溫(wen)(wen)(wen)(wen)高于此溫(wen)(wen)(wen)(wen)度(du)范(fan)圍(wei)(wei)時(shi)(shi)(shi)(shi)，組織(zhi)(zhi)容(rong)易(yi)脫水(shui)(shui)(shui)，可適(shi)當(dang)縮(suo)短脫水(shui)(shui)(shui)時(shi)(shi)(shi)(shi)間；而室(shi)溫(wen)(wen)(wen)(wen)低(di)于該溫(wen)(wen)(wen)(wen)度(du)范(fan)圍(wei)(wei)時(shi)(shi)(shi)(shi)，應適(shi)當(dang)延長(chang)脫水(shui)(shui)(shui)時(shi)(shi)(shi)(shi)間（如(ru)(ru)能(neng)保證在一(yi)個(ge)恒定的(de)(de)溫(wen)(wen)(wen)(wen)度(du)下(xia)最佳）。更(geng)換試劑(ji)，應以量(liang)為(wei)基礎，定量(liang)更(geng)換，不(bu)能(neng)等到(dao)切片不(bu)好(hao)時(shi)(shi)(shi)(shi)再去更(geng)換。否則，至(zhi)少會有(you)2～3批組織(zhi)(zhi)切片不(bu)好(hao)。根據我(wo)(wo)科經(jing)驗，如(ru)(ru)試劑(ji)用(yong)量(liang)為(wei)500ml，每500個(ge)蠟(la)塊更(geng)換一(yi)次為(wei)宜。