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SCIENCE. 



[N. S. Vol. XXIV. No. 608. 



that such digestive vacuoles may burst and 

 so pour out into the polyp's stomach a di- 

 gestive juice which will act on food particles 

 outside the substance of the cells, and thus 

 by the substitution of this process of out- 

 pouring of the secretion for that of inges- 

 tion of food particles into the cells we get 

 the usual form of digestion by juices se- 

 creted into a digestive cavity. Now this 

 being certainly the case in regard to the 

 history of the original phagocytes lining 

 the polyp's gut, it does not seem at all un- 

 likely, but on the contrary in a higher de- 

 gree probable, that the phagocytes of the 

 blood and tissues should behave in the same 

 way and pour out sensitizers and opsonins 

 to paralyze and prepare their bacterial 

 food. And the experiments of Metchni- 

 koff's pupils and followers show that this 

 is undoubtedly the case. Whether there is 

 any great variety of and difference between 

 'sensitizers' and 'opsonins' is a matter 

 which is still the subject of active experi- 

 ment. Metchnikoff's conclusion, as re- 

 cently stated in regard to the whole prog- 

 ress of this subject, is that the phagocytes 

 in our bodies should be stimulated in their 

 activity in order successfully to fight the 

 germs of infection. Alcohol, opium, and 

 even quinine, hinder the phagocytic action ; 

 they should, therefore, be entirely eschewed 

 or used only with great caution where their 

 other and valuable properties are urgently 

 needed. It appears that the injection of 

 blood-serum into the tissues of animals 

 causes an increase in the number and ac- 

 tivity of the phagocytes, and thus an in- 

 crease in their resistance towards patho- 

 genic germs. Thus Durham (who was a 

 pioneer in his observations on the curious 

 phenomena of the 'agglutination' of blood- 

 corpuscles in relation to disease) was led 

 to suggest the injection of sera during 

 surgical operations, and experiments re- 

 cently quoted by Metchnikoff seem to show 

 that the suggestion was well founded. 



After years of opposition bravely met in 

 the pure scientific spirit of renewed experi- 

 ment and demonstration, Metchnikoff is at 

 last able to say that the foundation-stone 

 of the hygiene of the tissues— the thesis 

 that our phagocytes are our arms of de- 

 fence against infective germs — has been 

 generally accepted. 



Another feature of the progress of our 

 knowledge of disease — as a scientific prob- 

 lem — is the recent recognition that minute 

 animal parasites of that low degree of uni- 

 cellular structure to which the name 'pro- 

 tozoa' is given, are the causes of serious 

 and ravaging diseases, and that the minute 

 algoid plants, the bacteria, are not alone in 

 possession of this field of activity. It was 

 Laveran— a French medical man— who, 

 just about twenty-five years ago, discov- 

 ered the minute animal organism in the 

 red blood-corpuscles, which is the cause of 

 malaria. Year by year ever since our 

 knowledge of this terrible little parasite has 

 increased. We now know many similar to, 

 but not identical with it, living in the blood 

 of birds, reptiles and frogs. 



It is the great merit of Major Ross, 

 formerly of the Indian Army Medical 

 Staff, to have discovered, by most patient 

 and persevering experiment, that the ma- 

 laria parasite passes a part of its life in the 

 spot-winged gnat or mosquito {Anopheles) , 

 not, as he had at first supposed, in the com- 

 mon gpat or mosquito (Culex), and that if 

 we can get rid of spot-winged mosquitoes 

 or avoid their attentions, or even only pre- 

 vent them from sucking the blood of ma- 

 larial patients, we can lessen, or even abol- 

 ish, malaria. 



This great discovery was followed by 

 another as to the production of the deadly 

 'Nagana' horse and cattle disease in South 

 Africa by a screw-like, minute animal para- 

 site, the Trypanosoma Brucei. The Tsetze 

 fly, which was already known in some way 

 to produce this disease, was found by 



