Maech 9, 1906.] 



science: 



367 



aminer has displaced, with great advantage 

 to all concerned, the aforetime local coroner. 

 And if, as there is much reason to suspect, 

 local influences and prejudices make it al- 

 most everywhere difScult to secure able and 

 aggressive local boards of health, then the 

 experiment should be tried of having dis- 

 trict, county or state officials, authorized 

 and willing to do the necessary sanitary 

 work. The present plan is a failure ex- 

 perimentally demonstrated ; let us continue 

 to invoke the experimental method, in 

 which we believe, but abandoning our pres- 

 ent customs, which have been experiment- 

 ally proved— for the thousandth time — to 

 be hopeless, and trying something more 

 promising. We can not do much worse; 

 we ought to do much better. 



William T. Sedgwick. 

 Massachusetts Institute of Technologt. 



SYMPOSIUM ON YELLOW FEVEB AND OTHER 

 INSECT-BORNE DISEASES. 



The Protozoan Life-Cycle: Gary N. Cal- 

 kins. 



The wonderfully successful results ob- 

 tained in New Orleans in the struggle 

 against Stegomyia fasciata has shown that 

 in yellow fever, as was long the case in 

 smallpox, pr(>tective measures may be un- 

 derstood and applied, although the specific 

 cause of the disease is unknown. 



I do not intend to discuss the question 

 as to whether this specific cause is a bacillus 

 or a protozoon, nor to consider the various 

 organisms that have been found in infected 

 yellow-fever mosquitoes. I purpose, rath- 

 er, to speak upon some of the general bio- 

 logical phenomena distinctive of protozoa, 

 and of the variations in vitality at different 

 periods of the life-cj'cle, and then' to point 

 out in how far the present data regarding 

 the yellow-fever organism agree with these 

 established facts. 



The protozoa are minute animals, con- 

 sisting for the most part of single cells 



having an independent life. They vary in 

 size from minute forms, too small to be 

 seen with the highest powers of our mod- 

 ern microscopes, to giant forms from two 

 to three inches in diameter. The vast 

 majority thrive in seas and lakes, stagnant 

 pools and ditches, and are absolutely harm- 

 less to man ; indeed, they become a boon to 

 him by giving to thousands of microscopists 

 the materials for a fascinating pastime. A 

 small minority are parasitic, but these few 

 cause vast epidemics among silkworms, fish, 

 and domestic animals, and have been the 

 means of great economic loss, or, through 

 malignant human epidemics, have terror- 

 ized whole communities and have brought 

 about untold loss of life. 



A protozoon rarely retains its individu- 

 ality more than a few hours. It then 

 divides into two, or, in some cases, into a 

 larger number of daughter individuals. 

 The parent organism has not died, there 

 is no unicellular corpse, but the protoplasm 

 of which that organism was composed is 

 now distributed by division among two or 

 more individuals. The process is repeated 

 again and again, and thus it continues, a 

 repetition of growth and reproduction. We 

 can not speak, therefore, of the life-cycle 

 of an individual protozoon, but must con- 

 sider rather the protoplasm of which that 

 individual is composed. It is this proto- 

 plasm that goes on through generation after 

 generation of individuals, and through all 

 the phases that constitute the aggregate of 

 phenomena which has been termed the life- 

 cycle. 



It was formerly believed that this pro- 

 toplasm, having all of the necessary func- 

 tions required for an indefinitely continued 

 existence, gives to the protozoon the at- 

 tribute of an endless life — physical immor- 

 tality. Experiments made within compara- 

 tively recent times have shown, however, 

 that this is not true and that the protoplasm 

 of a given protozoon gradually loses its 



