266 



SCIENCE. 



[N. S. Vol. XIV. No. 346. 



over a row of fifty books, each retinal element is 

 excited in succession by each book, but we do 

 not see one book taking the place of the other, 

 but all the books side by side. Further, when 

 the eye sweeps over fifty books in 1/10 sec, 

 each book is seen, or appears to be seen, with 

 perfect distinctness, though if the books moved 

 at the same rate over the eye they would com- 

 pletely fuse together. Our perceptions in no 

 wise correspond to the physiological processes 

 in the eye, but are what they should be for 

 our safety and convenience. 



J. McKeen Cattell. 

 Columbia University. 



CIRCULAR OF INFORMATION IN REGARD TO 



THE CAUSATION AND PREVENTION 



OF 3IALARIAL FEVER. 



Recent investigations have shown that ma- 

 larial fever belongs to that class of diseases 

 which require for their transmission the active 

 intervention of a definite kind of mosquito, 

 i. e.. Anopheles. This genus is not the com- 

 mon one of this region, but is nevertheless 

 present in many localities. 



The organism causing malarial fever {Plas- 

 modium malarise) is probably a true parasite, 

 and, so far as we know at present, finds the 

 conditions necessary for its existence only in 

 the living human body and in this genus of 

 mosquito, the latter becoming infected by suck- 

 ing the blood from an infected human being. 

 The malarial organism having thus entered the 

 stomach of the mosquito, passes through cer- 

 tain changes in the bodj'^ of the infected insect, 

 and at the end of about ten days reaches the 

 poison gland. After this time, if the mosquito 

 bites another human being, the malarial organ- 

 ism is introduced into the circulation of the 

 latter and malarial fever follows. 



So far as we know certain localities are ' ma- 

 larious ' only because they furnish fayorable 

 conditions for breeding this mosquito. Mala- 

 rial fever would not occur in any malarious dis- 

 trict, unless some infected human being were 

 in it, or came into it and infected the mosqui- 

 toes, which in turn infected other human beings. 



Recent observations in the intensely malarial 

 districts in Italy and Africa have shown that 

 even newcomers in these regions who pur- 



posely expose themselves by living in the most 

 highly malarious area, for example the Roman 

 Campagna, do not develop malarial fever, if 

 they are carefully protected from the bites of 

 mosquitoes ; and further, it has been shown 

 that this disease may be produced with cer- 

 tainty in any locality if a mosquito of the 

 genus Anopheles is allowed to bite a person suf- 

 fering from malarial fever and then, after a 

 sufficient time, is allowed to bite a healthy per- 

 son. 



Certain simple precautions suffice to protect 

 persons living in malarial districts from infec- 

 tion : 



First. — Proper screening of the house to pre- 

 vent the entrance of the mosquitoes (after care- 

 ful search for and destruction of all those already 

 present in the house), and screening of the bed 

 at night. The chief danger of infection is at 

 night, inasmuch as the Anopheles bite mostly at 

 this time. 



Second. — The confinement and continuous 

 screening of persons in malarial districts who 

 are suffering from malarial fever, so that mos- 

 quitoes may not bite them and thus become 

 infected. 



Third. — The administration of quinine in full 

 doses to malarial patients to destroy the malarial 

 organisms in the blood, and persistence in the 

 use of the remedy even for a few weeks after 

 apparent recovery. 



Fourth. — The removal of the breeding places 

 of the mosquitoes through drainage, filling up 

 of holes and surface pools, and emptying of tubs, 

 pails, etc., which contain stagnant water. 

 These mosquitoes particularly breed in surface 

 rain pools and surface stagnant water, where 

 there are no fish ; also exceptionally in pails, 

 tubs, barrels and tanks of standing water, 

 though they seem mostly to prefer natural ac- 

 cumulations. 



Fifth. — In pools which cannot be drained or 

 filled, the destruction of the mosquito larvse by 

 the use of petroleum thrown upon the surface, 

 by fhe introduction of minnows and other 

 small fish which eat the larvse, or by both 

 methods. 



These measures, if properly carried out, will 

 suffice greatly to restrict and largely to prevent 

 the occurrence of new malarial infections. 



