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SCIENCE 



[N. S. Vol. XXXVIII. No. ! 



the promised land, the land lying open to 

 the human view, so temptingly since the 

 first man looked up to the sky, but that a 

 few pathways are being mapped out, along 

 which we may direct a hopeful attack. 

 Our problems take a more definite form, 

 and even though we were never to solve 

 them completely, let us remember the words 

 of the poet: 



If God held in His right hand all truth, and in 

 His left nothing but the ever ardent desire for 

 truth, even with the condition that I should err 

 forever, and bade me choose, I would bow down 

 to his left, saying, "Oh, Father, give; pure truth 

 can be but for Thee alone. ' ' 



J. C. Kapteyn 



BLOOD PARASITES^ 



You will remember that Mephistopheles, 

 when he insists upon the bond with Faust 

 being signed with blood, says, ' ' Blut ist ein 

 ganz besondrer Saft" (Blood is a quite 

 special kind of juice). Goethe would prob- 

 ably not have used the word "Saft" had 

 he been writing "Faust" to-day instead of 

 in 1808, for at that time the cellular ele- 

 ments of the blood — although they had 

 been seen and described by Leeuwenhoek 

 in 1686 — were believed to be optical illu- 

 sions, even by so distinguished a person as 

 the professor of medicine of that time at 

 the Sorbonne. The incredulity of scien- 

 tific men as to what they see is proverbial 

 and astounding, fortunately ; but it is prob- 

 ably because science is really quite sure of 

 nothing that it is always advancing. 



I have the privilege this evening of try- 

 ing to show you the barest outlines of our 

 present' knowledge of the parasitology of 

 the blood. It is a subject of great prac- 

 tical and economic importance, as many 

 grave diseases of man and beast are caused 

 by these parasites, which, on account of 

 their minuteness, enormous numbers and 

 ' Abstract of a lecture before the Eoyal Institu- 

 tion of Great Britain, May 2, 1913. 



very complex life-histories, are very diffi- 

 cult to eradicate or to deal with prac- 

 tically. On this account there is a good 

 deal of the enthusiasm of the market-place 

 mixed up with this subject, which, al- 

 though a new one, has advanced with great 

 rapidity, and has revolutionized pathology 

 and medicine as far as possible. From our 

 point of view it began in 1880 with the 

 discovery by Laveran, in the military hos- 

 pital of Constantine, of the parasite which 

 causes malaria. This caused the protozoa, 

 to which order most of these parasites be- 

 long, to oust bacteria from the proud posi- 

 tion they then occupied of being the cause 

 of all the ills we have to bear, and to reign 

 in their stead; not an altogether desirable 

 change; for when you have seen what I 

 shall show you, you will agree with me 

 that sufficient unto life is the evil thereof. 

 It has had all the disadvantages of a new 

 subject, and since that time floods of work 

 have been poured into journals, annals, 

 proceedings, etc., some of it of the best, 

 with much of it that is indifferent, tem- 

 porary and bad; so that at times it seems 

 as if this branch of science were in danger 

 of being smothered in the dust 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 are 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 doubt- 

 ful generalizations, many of which we have 

 with pain and trouble to sweep into the 

 dustbin: 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 ter- 



