50 



KNOWLEDGE. 



[Makch 1, 1899. 



moving actively about by means of a series of curious jerks, 

 and occasionally coming to the surface to breathe. This 

 grub, which, by the way, differs from its parents in 

 possessing a pair of true biting jaws and no sucking 

 apparatus, soon transforms itself into an odd-looking 

 creature, which never takes food at all, for the reason 

 that it has no mouth. When the time comes for a 

 further change, the skin of this grotesque creature splits 

 open along the back, and out steps the dainty little gnat 

 . or mosquito, which, after drying its wings, flies oli'. to 

 commence (if it happens to be a female) its torturing 

 attentions to man or beast. 



As the name "malaria" (meaning "bad air") would 

 seem to imply, one of the earliest ideas was that the disease 

 originated by the inhalation of various noxious gases 

 which are generated in swampy districts. Decaying 

 vegetation was also supposed to be an active cause, as were 

 also great and sudden changes of temperature. The con- 

 nection of bacteria with the disease was first mooted about 

 the middle of the century, and by later researches has 

 been established without a doubt. The germ or bacillus of 

 malaria was first discovered in 1879, at Rome, by two Italian 

 investigators, and since that time their fellow-countrymen 

 have kept well to the front in the study of this important 

 subject. Although the bacterial nature of malarial fever 

 in its various forms has been thus clearly established for 

 some little time, the method of its dissemination remained 

 a mystery until the startling discoveries due to Grassi, 

 Bignami, and others. 



According to Prof. Grassi, the first person to hint at the 

 curious relations between mosquitoes and malaria was an 

 investigator of the name of Laveran, who latterly, however, 

 limited himself to the conception that infection took place 

 through the air or water, at the same time admitting that 

 the bacillus spent some part of its existence in a lower 

 animal or vegetable. Next, Dr. Manson supposed that the 

 germ was normally present in mosquitoes or in some other 

 sucking insect, and that on the death of the latter it would 

 commence a free life in the air or water, entering the 

 human body by inhalation or by the drinking of water. 

 Koch at first held a similar theory, but Bignami went a 

 stage further, and conceived the idea of inoculation by the 

 bite of the insect, which might be a gnat or some allied 

 insect inhabiting damp places. Last year Koch confirmed 

 the American researches, showing an analogy between the 

 behaviour of ticks in the propagation of the disease in 

 cattle known as Texas fever, and that of mosquitoes in 

 relation to malarial fever, both these diseases being due 

 to bacilli undoubtedly related to each other. Later still, 

 both JIanson and Ross have made some interesting com- 

 munications, the researches of the latter having reference 

 to germs in birds which also have a species of mosquito 

 as intermediate host. 



The first thing Grassi set himself to do, therefore, was 

 to find out what species of insect must be considered 

 guilty of spreading the disease. As he tersely remarks, 

 only some species can be culpable, because there are 

 districts notoriously teeming with mosquitoes and yet not 

 infested with malaria, while on the other hand the times 

 or seasons of these insects, and the appearance of the 

 disease do not always coincide. By a process of elimina- 

 tion the Professor sifted out the species until only a few 

 were left for further investigation as at any rate suspicious. 

 Among the results which followed, the two here given are 

 the most important : (1) three species of gnat or true 

 mosquito must certainly be regarded with great suspicion, 

 and (2) Culex pipiens, whose life-history we have briefly 

 sketched above, must be considered harmless. 



With regard to Culex pipiens, Grassi reports that this 



species is the predominating one in non-malarial districts, 

 while, on the other hand, it is scarce, or even wanting alto- 

 gether, in not a few districts infested with the fever. Further 

 confirmation of its innocence is also found in the following 

 case cited by the Professor, as observed at Follonica, in Tus- 

 cany. This region is much infested by malaria, and in the 

 house which serves as hospital for the foundries there the 

 ground floor is set apart for the patients, while the upper 

 stories accommodate the medical staff. In August last, when 

 Grassi visited the place, the only species found there was 

 the one in question, and, in accordance with this fact, we 

 learn that the physicians never had to record the develop- 

 ment de novo of a single case of malaria. On the contrary, 

 among the workmen of the foundry who live a little dis- 

 tance away, the cases of fever were in daily evidence. By 

 searching in their houses certain of the suspected species 

 were found, which evidently accounted for the presence of 

 the disease. 



Unfortimately, the various species of mosquito have no 

 English names by which they can be distinguished. There- 

 fore, in speaking of the three more particularly concerned 

 in the question now before us, we shall be compelled to 

 use their scientific names. These names are Anopheles 

 clavifier, Cule.r penicillarig, and Culex malarice. Of these, the 

 first, which we shall refer to simply as Anopheles, according 

 to Grassi, is constantly found in all malarial districts, and is 

 much more frequent where the disease rages more fiercely. 

 It may be distinguished from its relatives by having its 

 wings spotted, with the spots arranged so as to form a 

 capital letter T. Grassi calls it a " spy " of malaria, and 

 says that the relations between it and the disease have 

 been confirmed in Lombardy, Tuscany, the Roman Cam- 

 pagna, and in many other places. After giving the details 

 of many cases where the disease and the insect either 

 co-exist or are both absent, he refers to a locality near 

 Saronno, where in the middle of a healthy district is a 

 small circumscribed area infested by malaria, and, curiously 

 enough, the Anopheles is found there, but not in the sur- 

 rounding healthy zone. A similar instance occurs near 

 the small lake of Ceriano. 



The rice-fields are veritable hot-beds of malaria, and 

 mosquitoes are exceedingly abundant there, too. An ex- 

 ception in both respects occurs near Veniano, where there 

 is a very small rice-field so deficient in regard to its water 

 supply that the rice does not prosper. Grassi found no 

 mosquitoes there, and the medical authorities, likewise, 

 have failed to record the presence of disease in its neigh- 

 bourhood. 



Up to the time of writing the first of the three papers 

 we are now summarizing, Grassi only found a single ex- 

 ception to the co-existence oi Anopheles and malaria. Near 

 Saronno there is an expanse of artificial swamp containing 

 a few mosquitoes, but cases of disease have not as yet been 

 reported. Considering, as Grassi says, that the swamp is 

 artificial and relatively recent, it can be readily seen that 

 the opportunities afforded to the insects of becoming infected 

 have not been frequent, as owing to the peculiar situation 

 of the swamp very few persons have been bitten. 



The second species, which bears the name of Culex 

 penicillaris, is also undoubtedly instrumental in spreading 

 the disease, especially in September, when the Anopheles 

 begin to diminish in numbers. This species is more 

 frequent, too, in places troubled by September malaria. 



The third species put down as guilty appears to Grassi 

 to be a new one, and he, therefore, gives to it the very 

 appropriate name of ( 'ulex malaria. 



As to the time of day when the insects bite, our author 

 states that the Anopheles prefers to attack within an hour 

 on either side of sunset. In about an hour and a half at 



