370 



SCIENCE. 



[N. S. Vol. XXIII. No. 584. 



indicates that processes are taking place in 

 the development of the germ which can be 

 explained only on the supposition that con- 

 jugation phenomena, analogous to those in 

 the malaria mosquito, are taking place, and 

 this supports the view that in the human 

 blood the organisms are endowed with a 

 high potential of vitality. Again, the fil- 

 tration experiments in which it has been 

 demonstrated that the organisms may pass 

 through the finest filters known to us, indi- 

 cate that the organism is among the small- 

 est of living things, and belongs to that 

 group which is rapidly becoming more than 

 hypothetical, the ultra-microscopic forms. 

 The small size may be a result of rapid 

 multiplication, and it is not improbable 

 that after the incubation period larger 

 forms will be recognized in the digestive 

 tract of the mosquito and in the salivary 

 glands. 



Finally, if the organism is a protozoon 

 there is only a limited possibility as to its 

 systematic position. Larger forms like 

 Trypanosoma would not pass the finest 

 filters; corpuscular parasites like Piro- 

 plasma would likewise be filtered out, be- 

 sides which the yellow-fever organism is 

 known to be a plasma parasite. A single 

 genus of protozoa is known at the present 

 time that fulfills all of the conditions of 

 the yellow-fever organism ; amongst its spe- 

 cies are some that are at times ultra-micro- 

 scopic ; that have a characteristic change of 

 hosts from warm-blooded forms to mosqui- 

 toes and that are characterized by remark- 

 able virulence. This is the genus Spiro- 

 chceta and in it alone, at the present time, 

 do we find the type that satisfies all of the 

 conditions known of the organism of yel- 

 low fever. 



Dr. James Carroll said in discussing 

 Professor Calkins 's paper: "I have listened 

 with the greatest interest to Professor Cal- 

 kins 's exposition of the life histories of 

 protozoa and I am reminded by it of a 



series of hypothetical experiments that for 

 some time I have felt a great desire to 

 see performed and which might throw a 

 flood of light on the nature of the para- 

 site of yellow fever. Seasoning from the 

 standpoint that the organism is an obli- 

 gate animal parasite, a series of passages 

 through the human being by means of 

 direct inoculations with blood, without the 

 intervention of the mosquito, should gradu- 

 ally bring about attenuation or eventually 

 render it incapable of further reproduction 

 in man, by restricting its existence to a 

 single phase of its life-cycle. Such a result 

 would almost conclusively indicate the king- 

 dom to which it belongs, but the deterring 

 factor is, of coui-se, the risk to human life. ' ' 



( =p -J. V ''"' """^'^^w ."WV 



Filariasis and Trypanosofhe Diseases: 



Henry B. Ward. 



The presence of microscopic nematodes 

 in the blood was recognized as early as 

 1872, though their separation into distinct 

 species has not even yet been fully accom- 

 plished. The best known of these embry- 

 onic forms is that belonging to Filaria ian- 

 crofti; it was shown by Manson to manifest 

 definite periodicity in its occurrence in the 

 peripheral circulation, and hence was desig- 

 nated Filaria nocturna. During the day 

 this form retires to the capillaries of the 

 lungs. For further development it must 

 be taken up into the stomach of a mosquito, 

 from which it wanders out actively into the 

 thoracic muscles and there assumes a qui- 

 escent stage. There appears to be no defi- 

 nite generic adaptation as in the case of the 

 malarial and yellow fever organisms, but 

 various species of Culex and Anopheles 

 may serve as intermediate hosts. After a 

 period of rest and growth covering four- 

 teen to twenty days the larvag become mi- 

 grants and move through the lacunae of the 

 body into the proboscis. The precise 

 method of transference into a new host is 

 not yet clearly demonstrated, but the filariae 



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