1905.] Kala-Azar, etc., from Leishman-Donovan Bodies. 291 



mosquitos, but, in my experience such skin affections are too rare to alone 

 account for the frequency of infection. Further consideration will, I think, 

 show that the difficulty in finding these minute parasites in the peripheral 

 blood does not necessarily exclude the possibility of their occurring there 

 in sufficient numbers to infect insects, especially during high fever, when 

 they have been found in circulating leucocytes. In the first place, it has 

 been shown, by Christophers especially, that the organisms multiply in the 

 endothelial cells lining the blood-vessels of the internal organs, such as the 

 spleen, liver, and bone-marrow, and when numerous, in films obtained by 

 spleen puncture, they are frequently seen in groups in fragments of these 

 cells, which during life must frequently rupture and set them free in the 

 circulation, as is also proved by the same observer having found them in the 

 blood of some of the large veins. It is further of interest to note that the 

 endothelial cells of these very same organs are the principal sites of the 

 deposits of malarial parasites in the internal organs, while I have also 

 several times found Leishman bodies in the brain (where malarial parasites 

 also occur), so that it is clear that they must frequently enter the circulating 

 blood in considerable numbers. Secondly, the human stage of the parasite 

 is so small that it would be scarcely easier to find in the blood by micro- 

 scopical examination alone that typhoid bacilli in that disease, although the 

 latter can be readily obtained by cultural methods. 



The great difficulty of finding the human stage of the Hepatomonas of 

 kala-azar in the blood, even if present in sufficient numbers to infect 

 suitable insects, is well shown by Novy and MacNeil's(12) experience of 

 searching for trypanosomes in birds ; for while they only succeeded in 

 detecting this large actively moving parasite by microscopical examination 

 of thick blood films in 8 per cent., nevertheless they cultivated the parasite 

 on their blood-agar medium in 50 per cent, of the same series. Moreover, 

 even when they found them by their movement in thick fresh films, yet in 

 the same birds they frequently failed to detect them in stained specimens. 

 How much more difficult would it be to demonstrate the minute motionless 

 Leishman bodies, which can be only seen in thin stained films, even if they 

 were present in relatively large numbers in the peripheral blood ? 



Thirdly, the extremely rapid multiplication of the flagellated forms in 

 some of my recent cultures would appear to indicate that, in the presumably 

 still more favourable natural conditions of the extra-corporeal stage of the 

 parasite, a very small number of the human organisms would multiply to 

 such an extent as to constitute a powerful infective agency. 



The only reasonable alternative to the hypothesis just set forth is the 

 suggestion of Manson, Christophers, and others, that the organism may escape 



