1913] on Blood-Parasites 749 



because it finds it is not in the stomacli of the insect it intended to 

 be in, but between two pieces of glass. 



From Htemoproteus it is easy to pass to a rare and undeter- 

 mined parasite of the blood of birds called a Leucocytozoon. It 

 occurs in the blood in the form of a long, spindle-shaped, unpig- 

 mented body. Very little is known of it except that it is found in 

 its sexual forms. The earliest observers of this parasite— Danilewsky 

 and Ziemann — believed the host-cell to be a leucocyte (hence the 

 name), but Laveran has shown that it is a red corpuscle. 



We now come to a group of parasites of great practical import- 

 ance, the Babesias, formerly called Piroplasma, which are the cause 

 of Texas fever or red-water fever, malignant jaundice. East Coast 

 fever, and biliary fever amongst domestic animals. We know, again, 

 little that is certain concerning this group, except that they are un- 

 pigmented parasites of the red corpuscles, and are carried by ticks. 

 They are the most destructive to the blood of any we know. In an 

 ox, I have seen the red corpuscles decrease from 8,000,000 — the 

 normal — to 5G,000 per cubic millimetre in two days. 



Another important group, the Leishmania, is still uncertain 

 of its exact position. In the body they occur as small bodies with a 

 nucleus and micro-nucleus, but when cultivated on artificial media 

 they become flagellated organisms of a herpetotomas type. It is not 

 quite certain what insect plays the part of carrier, but the different 

 varieties of this group cause the diseases known as Kala Azar or 

 tropical splenomegaly, Oriental sore, Delhi boil, Biskra boil, etc., and 

 also infantile splenic angemia. 



The last class are the Haemogregarines. These are parasites 

 of the red corpuscles of reptiles principally, but they have been 

 described in mammals and birds. We only know certain stages of 

 the greater part of them : they are large, sausage-shaped bodies, not 

 pigmented, and they are supposed to be carried by leeches, ticks, lice, 

 and fleas. They generally have a capsule. In some instances the 

 host-cell is enormously enlarged and entirely de-hgemoglobinized, but 

 in most cases the host-cell is not enlarged. 



I have now taken you over some examples of all the known types 

 of blood-parasites, but, at best, the picture in your minds must be 

 like that of a landscape taken from a railway carriage at full speed ; 

 and the result, I fear, only a kind of clarified confusion, but it will 

 be something if I have succeeded in making it transparent at the 

 edges. What must have struck you most is the smallness of our 

 exact knowledge of many of these extraordinary organisms and the 

 gaps that there are even in this. But the incitement to future work 

 lies in this fact, for 



" Things won are done, joy's soul lies in the doing." 



[H. G. P.J 



