744 Mr. Henry George Plimmer [May 2, 



(4) Eosinophiles. — These are characterized by a bilobed nucleus, 

 and by granulations which colour deeply with eosin and other acid 

 colours. 



(5) Labrocytes or Mastzellen. — These are rare, and are charac- 

 terized by large granulations which stain with basic colours. 



In parasitic diseases these corpuscles are profoundly modified and 

 altered, numerically and morphologically, and other new elements 

 may make their appearance in the blood. 



The blood is essentially the same in all animals, but it varies 

 within certain limits. For instance, the red corpuscles are not of the 

 same size and shape in every animal, and in birds and fishes they are 

 nucleated ; in us they are only nucleated in foetal life and in disease. 

 The mononuclear and polynuclear leucocytes are really separate 

 organisms living in us, and they have qualities which it is very 

 difficult to call anything else but consciousness ; so that it is a subtle 

 distinction to draw the line between the parasites — which these Onco- 

 cytes, are, in a way — which are part of us, and those that are not. 

 When the balance of power is well preserved amongst our leucocytes, 

 when they are working well together, then all is well with us ; if we 

 are ill, it is because they are quarrelling with themselves or with an 

 invader, and we send for Sir Almroth Wright to pacify or chastize 

 them with his vaccines. 



So that, as Darwin said : " An organic being is a microcosm, 

 a little universe, formed of a host of self-propagating organisms, 

 inconceivably minute and numerous as the stars in heaven " — as we 

 ourselves are but parts of life at large. 



The three main functions of blood are : that it is a means of 

 respiration, a means of nutrition, and a defence against invading 

 organisms. 



And now to these latter. A blood-parasite proper is a living 

 being, vegetable or animal, passing part or the whole of its existence 

 in the blood of another living being, upon which it lives, this being 

 obligatory and necessary to its life-cycle. 



It was in 1841 that the first blood parasite was seen by Valentin 

 in the blood of a fish, and two years later Gmby gave the name 

 Trypanosoma to an organism he found in the blood of a frog. But 

 since Laveran's discovery of the malarial parasite in 1880, we have 

 learnt to differentiate many other parasites as causal agents of such 

 diseases as I shall mention later in connexion with the various 

 parasites. But we know as yet dangerously little about most of 

 them, so that we have strenuously to resist the temptation to 

 make our account of them sound too harmonious, before we 

 have found half the notes of the chord we are trying to play. 

 We speak, as it were, with authorized uncertainty, and there 

 are parts of our science which, after all, are only expressions 

 for our ignorance of our own ignorance. These parasites have 

 a very complicated life-history ; part of their life-cycle is passed 

 in the blood of man or beast, and part in various parts of the body 



