191;}] on Blood-Parasites 747 



into some soluble form, taking, in a horse, for instance, four days to 

 dispose of one dose, and the effect of this is much more profound and 

 lasting than that of the salts. But some trypanosomes always escape, 

 since one dose is never sufficient for cure. In rats with nagana, in 

 which the trypanosomes by the fifth or sixth day may number 

 3,000,000 per cubic millimetre of blood, the minimum number of 

 doses for cure has been found to be four, and with this dosage it is 

 possible to cure 100 per cent of rats. So there is still some hope. 



It is interesting in this connexion to remember what Bacon, 

 whose death, you know, was due to an experiment he undertook to 

 prove the preservative action of intense cold upon animal bodies, 

 says, " Laying aside therefore all fantastic notions concerning them, 

 I fully believe, that if something could be infused in very small 

 portions into the whole substance of blood ... it would stop not 

 only all putrefaction, but arefaction likewise, and be very effectual 

 in prolonging life." His vision was prophetic ! 



The bird trypanosomes are very much larger than the mam- 

 malian variety, are very dense, and move much more slowly. 



An example of an organism very closely allied to the trypano- 

 somes which is only found in fishes' blood, and is called a Trypano- 

 plasma, has two flagella, and the micro-nucleus is very large. They 

 are probably transferred by leeches, but very little is yet known of 

 them. 



There are other flagellated organisms which may appear in the 

 blood and live there as accidental parasites. There is a kind of 

 inflammation of the intestines in reptiles (in the large sense) which 

 causes the mucosa of the intestine to become permeable, so that 

 some of the organisms which live in the intestine are able to get into 

 the blood and live there. The only mention of these organisms in 

 the blood is by Danilewsky, who in 188!) found hexamitus in the 

 blood of a frog and tortoise. When in the blood they appear to 

 excite a general oedema and ascites. I have found them now in 

 nine cases. These are interesting as showing the power of adaptation 

 to new surroundings possessed by these parasites. 



I now come to the intracellular parasites. 



Schaudinn thought that the bird trypanosomes had an intra- 

 cellular stage, and if this were so they would form a bridge between 

 the extracellular parasites, of which I have shown you types, and 

 the intracellular parasites we are about to consider. But Schaudinn 

 seemed, with his very brilliant attainments, to want a little more 

 ballast of medical earth-knowledge. His work on this point has 

 not been confirmed, and he was probably misled by a double, or 

 even treble infection, so that we must think of these intracellular 

 parasites as quite distinct from the others. 



I will take first the Plasmodium prascox, the cause of the malaria 

 in birds, as this parasite is of great historical interest ; for it was 

 Ross's work on this organism and his discovery of the rest of its life- 

 cycle in the mosquito, which enabled him — on account of the great 



