im?)] on Blood-Parasites 743 



if this branch of science were in danger of being smothered in the 

 dnst of its own workshop, or drowned in the waters of its own 

 activity. We do not, nowadays, keep our ideas and scraps of work 

 to ourselves until they ai'e either established or, as is more likely, 

 dissipated, so we have a huge mass of what is called " literature," 

 filled with many trivial, fragmentary and doubtful generalizations, 

 many of which we have with pain and trouble to sweep into the dust- 

 bin : Nature's blessed mortmain law taking too long to act. You 

 remember Carlyle complained — to use a mild term — of Poggendorff's 

 " Annalen,' and I feel sure that, if he had had to study blood-parasites 

 now. he would have said that it was a much over be-Poggendorffed 

 subject. Blood-parasites are afflicted, too, with terrible names, and 

 with large numbers of them ; some have as many as ten or even 

 fifteen different names, perhaps on the Socratic principle, that naming 

 saves so much thinking. And they are in Latin, too, so that the 

 terminology of this subject is a perfect museum of long Latin and 

 hybrid-Latin names. The terminology generally of our later biology 

 is, as one has said, " the Scylla's cave which men of science are pre- 

 paring for themselves, to be able to pounce out upon us from it, and 

 into which we cannot enter." This will be my excuse if I should 

 use words you do not understand. 



I will just remind you of the structure of the blood, that it con- 

 sists of an extraordinarily complex fluid — the plasma — which holds in 

 suspension living cellular bodies, called cells or corpuscles. These 

 are of two kinds, red and white corpuscles. The red are by far the 

 more numerous, and in man there are about 5,000,000 of them to a 

 cubic millimetre of blood, but this number varies enormously under 

 the influence of parasites. To these red corpuscles is due the red 

 colour of the blood, and they are the carriers of oxygen, acquired by 

 the aeration of the blood in the lungs, to the tissues. We breathe in 

 order that they may breathe, for we only care about oxygen in so 

 far as they care about it. 



The other kind of corpuscles are the white, or leucocytes, and 

 of these in health, there are about 7500 per cubic niillimetre. 

 A few years ago it was enough to know that there were red and 

 white corpuscles, but now we have to know more. Through the 

 work of Ehrlich we know that there are at least five different kinds 

 of leucocytes in normal blood, which I will just indicate to you. 



(1) Lymphocytes. — These are the smallest cells, and contain a 

 relatively very large nucleus. 



(2) Large Mononuclears. — These are large, and are called macro- 

 phages, as they possess the power of being able to absorb and digest 

 parasites and other foreign bodies. 



(3) Polynuclears. — These are characterized by the irregular, monili- 

 form aspect of their nucleus, and they are called microphages for the 

 same reason that the large mononuclears are called macrophages. 

 Both of these are also called generally, phagocytes, on account of 

 their power of ingesting and digesting foreign bodies. 



Vol. XX. (Xo. 107) 3 d 



