i6 



NATURE 



[August 23, 19 17 



three functions to study. First would come emigra- 

 tion, then phagocytosis, and lastly intracellular diges- 

 tion. Emigration has up to the present been studied 

 only in the interior of the organism You will realise 

 that means that it has been studied only in a dithcult 

 setting and in the presence of all manner of disturbing 

 factors, and you will appreciate that we want now a 

 new and better technique. For Ave require for the 

 treatment of the infected wound to find out how best 

 to call out the leucocytes ; and how, when occasion 

 requires, to restrain their emigration. 



I have in connection with this a technique to de- 

 scribe to you ; but first I want you to appreciate what 

 we can and what we cannot expect from leucocytes in 

 the matter of locomotion. Leucocytes can, we know, 

 make their way out through small openings. They 

 can also travel over any ordinary surface. They can 

 edge their way along faster when lightly compressed 

 between two surfaces. They can crawl along strands, 

 creep through a meshwork, and climb a scaffolding. 

 But they are unable to climb a vertical glass wall. And 

 again, they are unable to swim, and so once they get 

 into open fluid they simply go to the bottom. We may 

 liken them to very minute slugs crawling along sur- 

 faces and climbing trellises, but brought up short by 

 any considerable barrier of fluid. 



! Fig. 4. — Drawing of four flattened capillarj' tubes. A, filled 



in with blood ; B, a similar tube after centrifugalisation 

 showing above the " white " and below the "red clot" ; 

 C and D, similar tubes after incubation. Leucocytic 

 emigration is in each case visible to the naked eye as an 

 opaque white band occupying the lower portion of the 

 white clot. In D, where physiological salt solution had 

 been imposed upon the white clot, the band of emigration 

 is much broader than in C. 



All these points must be considered when seeking for 

 a technique for the experimental study of emigration, 

 using for that study specimens of blood withdrawn 

 from the body. The containing blood-vessel can up to 

 a point be imitated by a glass tube, and we can, to 

 facilitate observation, use tubes drawn out flat, such 

 as. shown in Fig. 4. But the artificial differs from our 

 natural capillary in having impermeable instead of per- 

 meable walls. This, of course, makes emigration 

 through the walls impossible. None • the less, these 

 tubes supply what we want for the study of the move- 

 ments of leucocytes. We can institute races along the 

 length. 



But first certain preparations must be made. The 

 course must be cleared of all obstructions — i.e. the red 

 corpuscles must be got out of the way. Next the leuco- 

 cytes must all be brought back behind the scratch line. 

 Further, we must provide a scaffolding for the leuco- 

 cytes to climb. All this can be arranged. We fill in 

 our flat emigration tubes with blood and seal them at 

 one end. Then, by centrifuging, we bring the blood 

 fluids to the top and the corpuscles to the bottom. The 



NO. 2495, VOL. 99] 



lighter leucocytes will now have arranged themselves 



in a layer immediately above^ the red ; and presently 



the supernatant fluid will clot and the meshwork of 



fibrin will then provide the scaffojding we require. We 



can now impose upon the clot — let me for convenience 



call it the white clot — any chemical agent we please 



and let it slowly diffuse down to the leucocytes. For 



the study of the effect ot bacterial infection, we can 



introduce microbes into the blood before this is filled 



into the tube. Or, as an alternative, blood can be 



filled into tubes the walls of which have been wetted 



with a microbic culture. Finally, we set our experl 



ment going by placing our emigration tubes in the 



incubator — that is, we supply to our leucocytes tb 



necessary warmth. 



And we can at any 



moment take stock 



of what is occurring 



in our tubes by 



examining through 



the walls with the 



naked eye or with 



the low power of 



the microscope. 



Also, by a very 



simple technique we 



can extract the clot 



from the tube and 



mount and colour 



it, so as to bring 



everything clearly 



into view under the 



high powers of the 



microscope. 



Etnigration of Leu- 

 cocytes : Facts with 

 Practical Applica- 

 tion. 



I must limit my- 

 self to showing you 

 in connection with 

 emigration a few 

 outstanding facts 

 which have a prac- 

 tical application to 

 the treatment of 

 wounds. Let me 

 begin with the 

 naked-eye appear- 

 ances. We have In 

 Fig. 4, C and D, 

 emigration tubes 

 containing centri- 

 fuged blood which 

 has been in the 

 incubator for about 

 eight hours. In C 

 — the control tube 



d 



le.i 



1 



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H 



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Fig. 5. — Magrilied view of the band of leuco- 

 cytic emigraiion seen in Fig. 4, D. 



— we have centrifuged blood to which no addition has 

 been made. In D some weak salt solution has been 

 imposed upon the white clot. The emigrating leuco- 

 cytes are visible to the eye in the form of a slightly 

 opaque white band extending upwards from, the red 

 into the white clot. You see that in D the corpuscles 

 have climbed higher than in C. 



Fig. 5 shows what such a band of emigrating leuco- 

 cytes looks like under the microscope. Instead of 

 the leucocytes being all, as you will see in the next 

 figure, congregated together behind the starting line, 

 they here are actively emigrating — the more active 

 outdistancing the others in the race. 



Fig. 6 shows what happens when 5 per cent, salt 

 solution is imposed upon the blood. That salt passes 



