^008 Journal of Applied Microscopy 



face to face are arranged conveniently before the operator. A pair of these is 

 picked up with forceps and an edge of them applied to the drop of blood. The 

 blood flows by capillarity between the two cover-glasses, which are then with- 

 drawn from the drop of blood, slid apart and turned up to dry as in the Ehrlich 

 method. The advantage of this method over the original method of Ehrlich is 

 the ability to gauge the amount of blood that is needed. By the method of 

 Ehrlich the amount of blood taken depends upon the size of the drop and the 

 judgment of the manipulator; by this method when the film of blood has spread 

 throughout between the two cover-glasses they are withdrawn from the drop of 

 blood and the supply instantly cut off. By this method preparations can also 

 b« made from more extensive flows of blood as are often unavoidably obtained 

 from the internal organs of the lower vertebrates. 



2, The Method of Smith, Mannaberg, and Others. — By this method a square 

 cover-glass, preferably held in a pair of clamp forceps, is touched at one corner 

 to the drop of blood and the edge applied to the surface of a second cover-glass. 

 The blood at the corner immediately flows along the whole line of contact, and 

 by drawing the first cover-glass held at an angle of 45° across the surface of the 

 second cover-glass, a thin film of blood is left on the latter. The use of the end 

 of a glass slid'C instead of the edge of a cover-glass is recommended by several 

 as a more convenient implement for spreading the blood. 



In my own experience preparations can be made more rapidly, with less 

 regard to the quantity of blood taken and thinner by this method than by the 

 method of Ehrlich ; all of which ara important advantages in the technique. 

 Preparations can also be made by this method from extensive flows of blood 

 and from the bone marrow. 



Ilorder (1899) recommends a piece of gutta-percha half an inch square for 

 receiving and spreading the blood. The gutta-percha is held in one pair of 

 Ehrlich forceps and a cover-glass in another pair. The blood, as it exudes in a 

 fresh drop, is touched by the edge of the gutta-percha, which is laid flat upon 

 and drawn across the cover-glass, commencing from the edge held by the for- 

 ceps. Cover after cover can be spread as rapidly as they can be picked up 

 with the forceps. 



II. FIXING THE PREPARATIONS. 



As the term " fixation " is generally employed in histological technique it 

 refers to the killing and preserving of the cytological elements and their struc- 

 ture, especially the finer structure of the nuclei, for microscopical study. In dry 

 blood films, fixation in this sense of the word is accomplished in the process of 

 rapid drying, and any subsequent treatment of the preparation has little effect 

 on the preservation of the cell structure. Various methods other than rapid 

 drying have, however, been recommended for killing and preserving the cyto- 

 logical elements of the blood. 



A. Fixing Fresh Blood. 



1. Alcohol. — Bizzozero (1882) and Cornil (1887) put the fresh, undried 

 blood films in absolute alcohol for one hour or more. 



