ii 7 
THE THICK-FILM PROCESS FOR THE DETECTION 
OF ORGANISMS IN THE BLOOD 
By RONALD ROSS 
IN the Journal of State Medicine, December, 1902, and the Lancet, January 10, 
1903, I described a method which facilitates the detection of parasites of the 
blood by enabling us to examine thick films of dried blood in place of the thin 
films now generally used for the purpose. Instead of spreading a small quantity of 
blood over a large area and then fixing the haemoglobin and staining, the proposed 
method consists in taking a comparatively large quantity of blood, scarcely spread 
out at all over the slide, and stained without fixing the haemoglobin. In the first 
method one is often compelled to search many fields before finding a parasite : in the 
second method the parasites are much more crowded together owing to the thickness 
of the film of dried blood employed ; and are just as visible as in the thin film owing 
to the fact that the haemoglobin, the opaque element of the blood, not being fixed, 
has been washed out during the process of staining with aqueous stains. 
Photographs of a preparation of malarial blood made by this method were 
published in the Journal of Tropical Medicine, February 2, 1903 ; and Ruge has 
verified and amplified the process in the Deutsche Med. Woch, March 19, 1903, 
S. 205. Recently Bell and Laing advocate it for the detection of plague bacilli in 
blood [Lancet, June 20, 1 903) ; and I am confident that it will be found useful for 
diagnosis in many affections besides malaria. 
I now give a water-colour drawing of a field of a thick-film preparation of 
blood taken from an ordinary case of aestivo-autumnal infection. In a thick-film 
preparation of the same blood, less than one parasite on the average could be found 
in each field ; whereas it will be seen that about eighty parasites can be counted in the 
field given in the plate. The photograph shows a field of a thick-film preparation of 
rat's blood containing Trypanosoma brucei. In a thin film of the same blood only 
one or two parasites could be found per field. 
I am now using the following stock formulae for staining : — 
Eosine, 1 gramme Medicinal Methylene Blue, 10 grammes 
Water, 1,000 c.c. Sodium Carbonate, 5 grammes 
Water, 1,000 c.c. 
