416 V. CLIFFORD DOr.ELL. 



a carefully cleaned, glass slide (or coverslip) by means of a 

 platinum loop. I then place a drop of 1 per cent, osmic acid 

 or strong foi'inol (40 per cent, formaldehyde, Scheriug) beside 

 the first drop, and then mix both together and. spread the 

 fluid in a thin and even film on the slide. I then allow the 

 film to diT, which usually takes a few minutes. No heating 

 should be used to accelerate the process. The slide or 

 coverslip Avith the dried film is then placed in absolute alcohol 

 for about ten to fifteen minutes. It is then removed, and the 

 film allowed to dry once more. I then stain the filui with 

 Giemsa's or Leishman's stain in tlie usual way. After 

 staining I differentiate in 30 per cent, alcohol — wash in distilled 

 water — dry by blotting Avitli a cigarette paper — and mount in 

 cedar wood oil or neutral Canada balsam. Chromatin 

 structures are coloured a bright red; the cytoplasm being 

 blue, lilac or pink, according to the degree of difffrentiation. 

 The structure of many Bacteria is revealed with remarkable 

 distinctness by this method — its chief disadvantage being that 

 the prepai'ations sooner or later fade, and cannot as a rule be 

 satisfactorily re-stained. 



The above method of fixation — which I term tlie drop 

 ra ethod — calls for some further comments. In the first place, 

 it might be urged that the drying which takes phice would 

 be liable to injure the organisms, and give rise to misleading 

 appearances. This is not so, however. If the Bacteria are 

 fixed with osmic acid or formol before dr^nng is allowed 

 to take place they are not plasmolysed or injured in any 

 way. It is only when drying takes place before fi xatiou 

 that such disastrous i-esults ensue. 



I have made many preparations by other methods as 

 controls. I have made wet films and fixed them by immersion 

 in 1 per cent, osuiic acid or formol : I have also made wet films 

 and fixed them by exposure to osmic vapour : and 1 have then 

 stained these films by modifications of Komanowski's method 

 and mounted them in balsam without allowing any drying to 

 take place at any stage in the proceedings (cf. Dubell, 1908). 

 The final results obtained in all these cases are almost in- 



